This is CNBC's live blog tracking developments on the war in Ukraine. See below for the latest updates. 

Fighting has intensified around Ukraine's capital, while Russian forces bombard cities across the country, killing civilians who are unable to escape.

Invading Russian troops have redeployed off the main road north of Kyiv, moving into towns and forests as Ukrainian defenders have thwarted their attempts to move south with air and ground attacks.

Ukraine's authorities accused Russia of preventing the evacuation of people from the heavily besieged port city of Mariupol in the south of the country. Conditions in the city are dire, with civilians trapped there. Food, water and electricity are scarce.

More than 1,500 people have died in Mariupol from siege attacks so far, the Associated Press reported Sunday, citing the mayor's office.

Ukraine President Volodomyr Zelenskyy said at a Saturday news conference that about 1,300 Ukrainian soldiers have been killed since Russia's invasion began.

The Kremlin escalated its threats to the West as well. Speaking to Russia's state-controlled media on Saturday, Deputy Foreign Minister Sergey Ryabkov warned that Western convoys shipping weapons to Ukraine's defenders are "legitimate targets."

NATO secretary general warns that Russia may use chemical weapons

NATO Secretary General Jens Stoltenberg warned on Sunday that Russia might use chemical weapons against Ukrainians, Reuters reported, citing an interview with a German newspaper.

Stoltenberg told Welt am Sonntag that such an attack would constitute a war crime, but that Russia appeared to be inventing advance justification for using chemical weapons.

"In recent days, we have heard absurd claims about chemical and biological weapons laboratories," said Stoltenberg, who added that the Kremlin was creating a false pretext to justify something that can't be justified.

— Ted Kemp

Russia wants to break Ukraine into 'pseudo-republics,' Zelenskyy says

Ukraine President Volodymyr Zelenskyy said in a nightly address that Russia is trying to break up the country by creating new "pseudo-republics," the Associated Press reported.

"The occupiers on the territory of the Kherson region are trying to repeat the sad experience of the formation of pseudo-republics," Zelenskyy said, according to AP. "They are blackmailing local leaders, putting pressure on deputies, looking for someone to bribe."

Zelenskyy said that Kherson city council members on Saturday rejected plans for a new republic. Kherson is in Ukraine's south and now under the control of Russian forces.

Before invading Ukraine in late February, Russia "recognized" the Ukrainian regions of Donetsk and Luhansk as new, independent countries.

Russia has supported a separatist war in the east of Ukraine since 2014.

— Ted Kemp

U.S. authorizes $200 million in new Ukraine defensive assistance

The latest round of U.S. military assistance to Ukraine will include weaponry to counter "armored, airborne, and other threats," U.S. Secretary of State Anthony Blinken said in a statement late Saturday.

The $200 million in aid brings the total security assistance for Ukraine from the United States to $1.2 billion.

"We salute the armed forces of Ukraine and all Ukrainian citizens who are defending their country with great skill, iron will, and profound courage," the secretary of state said.

The United States will continued to give humanitarian assistance as well, Blinken said.

— Ted Kemp

Russia will rely increasingly on mercenaries to fight Ukraine, U.K. Defence Ministry says

As losses mount for the Russian military in Ukraine, President Vladimir Putin will "be forced to draw on alternative sources" to reinforce his overstretched regular troops, the U.K. Defence Ministry said late Saturday.

In an intelligence update, the ministry quoted Putin as publicly welcoming "16,000 mostly Middle Eastern volunteers" to support his invasion of Ukraine.

Since late 2020, Syrian mercenaries have deployed alongside Russian proxy forces in Libya, the ministry said.

Russia also has experience fighting in cooperation with Syrians in support of strongman ruler Bashar al-Assad. Russia engaged in indiscriminate bombardment of Aleppo in 2016, Pentagon officials said at the time.

Moscow has already acknowledged using conscripted Russian soldiers in Ukraine. The U.K. ministry said this week that Putin is likely also turning to corporate mercenaries employed by Russia-based companies that provide them.

Russia's Foreign Ministry did not immediately respond to a request for comment.

— Ted Kemp

Ukraine tells IAEA that Russia is planning to take permanent control of nuclear power plant

The International Atomic Energy Agency said Ukraine told the nuclear agency that Russia is planning to take full and permanent control of the Zaporizhzhya nuclear power plant.

The Kremlin denied the allegation, according to the IAEA.

Petro Kotin, the president of Ukraine's nuclear power plant operator Energoatom, told the IAEA that roughly 400 Russian soldiers were present full-time at the plant. He also confirmed to the agency that the nuclear power plant is under the control of the Russian military forces' commander. Russian soldiers captured the plant a little over a week ago.

— Amelia Lucas

EBay suspends all transactions involving Russian addresses

EBay said it was suspending all transactions involving Russian addresses due to "service interruptions by payment vendors and major shipping carriers."

"We will continue to evaluate and make necessary changes to our policies and service availability as this situation evolves and hope for a rapid, lasting, and diplomatic solution to this crisis," a spokesperson said.

The company is taking a number of steps to support Ukrainians and sellers in the region, the spokesperson said. That includes waiving seller fees, protecting sellers from late shipment penalties and negative feedback and matching employee donations to organizations helping Ukraine.

The e-commerce company has already removed all products related to Russian President Vladimir Putin, citing its policy against items that promote or glorify hatred or violence.

— Jessica Bursztynsky

Israeli PM Naftali Bennett call with Zelenskyy

From NBC's Raf Sanchez:

Prime Minister Naftali Bennett and the President of Ukraine Volodymyr Zelenskyy spoke Saturday. The conversation, which lasted for over an hour, dealt with ways to stop the fighting in Ukraine and the efforts that Israel is making on the matter.

From Israeli PM's spokesperson.

Zelenskyy on calls with France and Germany: 'We must stop the aggressor together'

Ukrainian President Volodymyr Zelenskyy said in a tweet he spoke with German Chancellor Olaf Scholz and French President Emmanuel Macron on a range of topics Saturday.

Zelenskyy said the leaders discussed "countering the aggressor," crimes against civilians and prospects for peace talks. He also asked for help in releasing the mayor of Melitopol, Ivan Fedorov, who he said was taken captive by Russian forces.

"We must stop the aggressor together," Zelenskyy said on Twitter.

Scholz and Macron later spoke with Russian President Vladimir Putin.

— Jessica Bursztynsky

Ukraine says seven killed after Russia fired at evacuation convoy

Russian forces shot and killed seven civilians, including one child, on Friday while they were attempting to evacuate the village of Peremoha, the State Service of Special Communications and Information Protection of Ukraine said on Twitter.

The exact number of injuries is unknown, the agency said.

The Ukrainian government said the group of civilians killed, including six women and the child, were attempting to flee the village for Gostroluchcha along an agreed upon "green" corridor.

After the shooting, Russian occupiers "forced the remnants of the column to return to the village of Peremoha and did not let them out of the village," the agency said.

"At present, it is almost impossible to establish contact with them, as well as provide humanitarian and medical assistance," it added.

— Jessica Bursztynsky

Pro-Russian forces patrol Volnovakha

Pro-Russian forces patrol the town of Volnovakha, which has been devastated by Russia's invasion of Ukraine.

— Adam Jeffery

Biden authorizes $200 million in defense aid to assist Ukraine

President Joe Biden on Saturday authorized the secretary of State to provide up to $200 million in defense aid to assist Ukraine, including through military education and training.

— Annie Nova

Civilians flee Irpin as Russia moves closer to Kyiv

Civilians flee Irpin, a city near Ukraine's capital of Kyiv, as Russian forces close in.

— Adam Jeffery

Citizens undergo military training in Ivano-Frankivsk

Civilian volunteers receive military training in Ivano-Frankivsk, a city in western Ukraine.

— Adam Jeffery

UN says at least 579 civilians killed, more than 1,000 injured in Ukraine

At least 579 civilians, including 42 children, have been killed since Russia invaded Ukraine, the U.N.'s human rights office said. More than 1,000 people have been injured.

The majority of casualties have been caused by the use of explosive weapons that have a "wide impact area," including shelling from heavy artillery and multi-launch rocket systems, missiles and airstrikes, the agency said.

U.N. officials have said they believe actual casualties are "considerably higher," as reports in some areas are delayed and others are pending confirmation.

—Jessica Bursztynsky

Ukraine's Zelenskyy shows some optimism about talks with Russian officials

Ukrainian President Volodymyr Zelenskyy on Saturday expressed some optimism about recent discussions between Ukrainian and Russian representatives.

"They have started talking about something, not just throwing ultimatums," Zelenskyy said at a press conference, according to NBC News. "I believe that this is a fundamentally different approach and it should be so."

He called for a "peace process, the end of the war process." Zelenskyy said it would need to begin with a cease-fire.

He added that some leaders have been filled in on the communication between Russian and Ukrainian parties.

"Those who are in contact with the Russian leader have this and they need to speak up," he added. "I know that the signals from them are not bad in terms of the proposals that came from us."

—Annie Nova

Germany's Scholz, France's Macron call on Putin to cease fire

German Chancellor Olaf Scholz and French President Emmanuel Macron called for an immediate cease-fire and a diplomatic solution to the war in Ukraine during a 75-minute long call with Russian President Vladimir Putin, the German government said in a statement.

An Elysee source told NBC News the call was "very frank" and "very difficult." Putin gave no sign he would stop the war, the person added.

The two leaders talked to Putin after they spoke with Ukrainian President Volodymyr Zelenskyy earlier in the day.

—Jessica Bursztynsky

Western arms convoys to Ukraine 'legitimate targets' for Russian forces, official says

Russia warned the West against sending further arms to Ukraine, saying such arms convoys could now be considered "legitimate targets" for the Russian armed forces.

Speaking to Russia's Channel One broadcaster earlier, Russia's Deputy Foreign Minister Sergey Ryabkov issued a warning to the West that could lead to a direct confrontation between Russia and NATO.

"We warned the United States that pumping Ukraine with weapons from a number of countries orchestrated by them is not just a dangerous move, but an action that turns the corresponding convoys into legitimate targets," the deputy minister said, according to comments reported by Russia's state news agency TASS.

Ryabkov said there could be consequences to what he called the West's "thoughtless transfer" to Kyiv of weapons such as portable anti-aircraft missile systems and anti-tank missile systems, both of which have been supplied to Ukraine by several NATO members including the U.S. and U.K. 

— Holly Ellyatt

'We're not going to give any more airtime to the lies,' U.S. says at the UN

Representatives from Russia and the United States traded barbs during Friday's United Nations Security Council meeting.

The UN meeting, which was called by Russia, follows multiple claims by Russian officials that the United States is carrying out a secret biological weapons program in Ukraine.

Izumi Nakamitsu, the forum's High Representative for Disarmament Affairs, said Friday the UN is "not aware" of any biological weapons program in Ukraine.

U.S. Ambassador to the United Nations Linda Thomas-Greenfield also denied the allegations saying, "There are no Ukrainian biological weapons laboratories supported by the United States, not near Russia's border or anywhere."

Thomas-Greenfield then directed her comments to Russian Ambassador Vasily Nebenzya.

"I know that you expect me to respond but we're not going to give any more airtime to the lies," she said adding "It's beneath this council."

"There's only one aggressor here and that is Russia and we hope they will be able to find it in their conscience to end the attacks and stop the suffering of the Ukrainian people," she added.

Thomas-Greenfield's comments echo those of White House press secretary Jen Psaki, State Department spokesman Ned Price and Pentagon spokesman John Kirby.

– Amanda Macias

Ukraine's president demands release of Melitopol's 'kidnapped' mayor

Ukraine's President Volodymyr Zelenskyy has demanded the release of the Mayor of Melitopol who Ukraine accused Russian forces of kidnapping, and violating international law, on Friday.

In a video message on Saturday, Zelenskyy demanded the release of Mayor Ivan Fedorov who was allegedly blindfolded and led away from an office by Russian troops on Friday, according to a video posted by Ukrainian officials Friday.

NBC News has not been able to independently verify these claims and it's unclear who the people are in the video, when the video was shot, and who shot the video.

Zelenskyy said he had spoken about the alleged kidnapping to the leaders of France and Germany, Reuters reported.

Situated in southeastern Ukraine, Melitopol fell under Russian control very early on in the invasion. Russia has not commented on the alleged abduction.

Protests were held in Melitopol on Saturday in which residents called for the mayor's release.

— Holly Ellyatt

Ukraine's foreign ministry says mosque in Mariupol shelled by Russia

Russian forces have shelled a mosque in Mariupol where 80 adults and children had taken refuge, Ukraine's foreign ministry said on Saturday.

"The mosque of Sultan Suleiman the Magnificent and his wife Roxolana (Hurrem Sultan) in Mariupol was shelled by Russian invaders," the foreign ministry said on Twitter, adding that "more than 80 adults and children are hiding there from the shelling, including citizens of Turkey."

Ukraine has repeatedly accused Russia of blocking attempts to allow civilians to flee the besieged southern port city of Mariupol which Russian forces have surrounded and shelled for days.

Ukraine's foreign ministry did not say whether any people had been killed or injured in the shelling of the mosque. Russia has previously denied targeting civilians.

— Holly Ellyatt

Ukrainian military airfield southwest of Kyiv completely destroyed by Russian strike, mayor says

A Russian airstrike has completely destroyed a Ukrainian military airfield southwest of the capital Kyiv, the town's mayor said on Facebook Saturday.

In a video message on Facebook, Mayor Natalia Balasynovych said Russian rocket attacks had destroyed the airfield in Vasylkiv and that explosions at a nearby ammunition depot were ongoing after the Russian airstrike.

Her comments come after a Russian Defence Ministry spokesman Igor Konashenkov reportedly told Russian news agencies that its armed forces have destroyed 3,491 Ukrainian military infrastructure facilities to date during its "operation," as Russia calls its invasion of Ukraine.

Russian news agency Interfax quoted Konashenkov on Saturday as saying that "123 unmanned aerial vehicles, 1,127 tanks and other armored combat vehicles, 115 multiple rocket launchers, 423 field artillery and mortars, 934 units of special military vehicles" had been destroyed in total during Russia's "operation" against Ukraine.

Interfax also cited the Russian Defense Ministry as saying its forces had "disabled the military airfield" in Vasylkiv as well as a Ukrainian adio intelligence center in Brovary (on the eastern outskirts of Kyiv) "with a high-precision weapon strike." CNBC was not immediately able to verify the claims.

— Holly Ellyatt

Bulk of Russian ground forces around 15 miles from Kyiv's center, U.K. intelligence says

The bulk of Russian ground forces are now around 25 kilometers (15 miles) from the center of Kyiv, according to the latest intelligence update from the U.K.'s Ministry of Defence, with fighting continuing to the north-west of the capital.

"Elements of the large Russian column north of Kyiv have dispersed. This is likely to support a Russian attempt to encircle the city," the ministry said on Twitter Saturday morning.

"It could also be an attempt by Russia to reduce its vulnerability to Ukrainian counter attacks, which have taken a significant toll on Russian forces."

The ministry's latest assessment comes after satellite imagery appeared to show that a large Russian military convoy has fanned out through the towns close to Antonov airport on the outskirts of Kyiv, with howitzers thought to be situated in firing positions nearby. Ukrainian forces have heavily fortified the capital ahead of an expected Russian assault.

Beyond Kyiv, the Ministry of Defence said the cities of Kharkiv, Chernihiv, Sumy and Mariupol remain encircled and continue to suffer heavy Russian shelling.

— Holly Ellyatt

Russia not letting people out — or aid in — to besieged Mariupol, president says

Ukraine's President Volodymyr Zelenskyy accused Russia of refusing to let civilians out of the besieged city of Mariupol in southern Ukraine.

"Mariupol remains blocked by the enemy," Zelenskyy said in a televised address late on Friday local time. "Russian troops did not let our aid into the city and continue to torture our people, our Mariupol residents."

He said another attempt would be made on Saturday to deliver food, water and medicine to the city, which has been surrounded and shelled by Russian troops for days.

Zelenskyy said around 7,000 inhabitants of Bucha, Energodar, Hostomel and Kozarovichi managed to escape on Friday.

— Holly Ellyatt

Ukraine Ministry of Defense claims drone strike destroys 'enemy control point' near Kyiv

The Ukraine Ministry of Defense on Friday night posted a video which it says shows a Ukraine drone attack on the "enemy control point" near Kyiv.

"A few minutes ago, the enemy control point in the Kyiv direction was destroyed. Our Air Force is working!" the Ukraine ministry's post on Telegram said, according to an NBC News translation.

CNBC was unable to independently verify the content of the video.

A senior U.S. Defense official told CNBC on Friday that Russian forces near Kyiv have moved forward some of their rear elements, including troops and military equipment, but the frontline has not advanced on the capital.

Russian forces are about 10 miles (16 km) outside Kyiv's city center, according to the most recent Pentagon assessment.

CNBC received no response to a request for comment from Russian officials made over the weekend.

— Ted Kemp and Amanda Macias

Russia's 'dumb' munitions are likely to increase civilian deaths, UK ministry says

Russian aircraft are relying on unguided, "dumb" munitions to support their troops on the ground, raising the likelihood of Ukrainian civilians being killed and wounded.

Dumb bombs and rockets are less accurate than guided weapons, which means they're less likely to strike what they're aimed at and more likely to randomly hit something else.

Russia is using rockets and other weapons that fire from greater distances — so-called "stand-off" weapons — so its pilots can avoid being shot down, the U.K. ministry said in an intelligence update on Friday night local time.

"The staunch resistance of the Ukrainian air defence forces is compelling Russia to rely on 'stand-off' munitions to conduct attacks against targets deep inside Ukraine," the ministry said.

The ministry said Russian air and missile forces had carried out strikes on two cities in Ukraine's west in the last 24 hours.

Ukraine's Parliament reported strikes on Lutsk and Ivano-Frankivsk at around 6 a.m. and 7 a.m. local time respectively on Friday. Those locations are further west than most Russian attacks on Ukraine so far.

In a video message posted to Telegram on Friday morning, Yurii Pohuliaiko, head of the Lutsk regional council, said four rockets had been fired into the city's military airport, killing two soldiers and injuring six.

CNBC received no response to a request for comment from Russian officials made over the weekend.

— Ted Kemp and Chloe Taylor