Ukrainian President Says Russian Forces Advancing On Third Nuclear Plant, After Cease-Fire Fails

Ukrainian President Volodymry Zelenskiy has told U.S. lawmakers that Russian forces have seized two Ukrainian nuclear power plants and are advancing toward a third.

Zelenskiy told U.S. senators and aides in a video call on March 5 that the Yuzhnoukrayinsk nuclear power plant, located in Ukraine's southern Mykolayiv region, was under threat as Russia's invasion of Ukraine entered its 10th day.

The Zaporizhzhya nuclear plant, in southeastern Ukraine on the banks of a reservoir on the Dnieper River, was the source of international concern after it caught fire after being shelled and seized by Russian forces on the night of March 3-4.

The Chernobyl nuclear power plant, located north of Kyiv and site of the world's worst nuclear disaster in 1986, was captured by Russian forces on February 24, the first day of the Russian invasion.

Earlier on March 5, Ukrainian officials put on hold civilian evacuation plans in two besieged cities after reporting firing by Russian troops despite a Moscow claim to have ordered cease-fires around Mariupol and Volnovakha based on mutual agreement to allow humanitarian corridors.

Meanwhile, a third round of talks between Kyiv and Moscow are scheduled to take place on March 7.

Russian Foreign Minister Sergei Lavrov on March 5 indicated that Moscow was not optimistic about the outcome of negotiations, accusing Zelenskiy of harming the talks by trying to secure help from NATO, but that Moscow was ready for a third round.

Earlier on March 5, Ukrainian Foreign Minister Dmytro Kuleba said he was open to talks with Lavrov, but only if they were "meaningful."

In the video call, Zelenskiy also stressed to the U.S. lawmakers Ukraine's need for Eastern European countries to provide aircraft as his country tries to defend itself from increasingly heavy Russian bombardment.

It was earlier reported that some NATO countries with Soviet-made aircraft, which would be familiar to Ukrainian pilots, were considering providing them to Kyiv to help Ukraine secure its airspace. Bulgaria, Poland, and Slovakia have since firmly denied the reports.

Zelenskiy has called for Western forces to create a no-fly zone over Ukraine, but the idea of using U.S. or NATO warplanes to police Ukraine's skies has been rejected.

U.S. lawmakers said in the call that they were preparing a relief package to provide a further $10 billion in military and humanitarian assistance to Ukraine.

SEE ALSO: Why A No-Fly Zone Over Ukraine Probably Won't Fly

Officials in the strategic southern city of Mariupol announced via social media on March 5 that "due to the fact that the Russian side does not adhere to the cease-fire and has continued shelling both of Mariupol itself and its environs and for security reasons, the evacuation of the civilian population has been postponed."

"For security reasons, the evacuation is therefore postponed," Mariupol city authorities said via Telegram. They said talks were continuing with Russia on how to "ensure a safe humanitarian corridor."

Ukrainian Deputy Prime Minister Iryna Vereshchuk said in a video statement that Russia had "violated the agreement" and despite the mediation of the Red Cross "is shelling the city of Volnovakha."

Vereshchuk cited ongoing attacks with "heavy weaponry" and called on the Russian side to "cease shelling, restore the cease-fire, and allow the formation of columns of the humanitarian corridor so that children, women, and the elderly can leave the settlements."

She also urged Russia to provide an opportunity for humanitarian supplies including "medicine, insulin, and so on, as well as food" from the cities of Dnipro and Zaporizhzhya.

It was not clear that Russian bombardments stopped at any point.

Britain said on March 5 that the proposed cease-fire in Mariupol was likely an attempt by Russia to reset its forces and deflect international condemnation.

Russia's Defense Ministry said it had ordered at least a partial cease-fire in Mariupol and Volnovakha to allow humanitarian corridors for civilians to leave.

The ministry added that its 10-day-old offensive around the rest of the country was continuing in Ukraine, where international bodies are already investigating accusations of war crimes and other offenses against civilians.

WATCH: Hundreds of people with Ukrainian flags gathered on the main square in Kherson, chanting against the Russian invasion. Russian forces have seized control of the city in southern Ukraine.

Ukrainians Wave Flags At Protest In City Seized By Russian Forces

A senior Ukrainian government adviser had suggested more agreements would follow to let civilians evacuate other areas. "There will definitely be more agreements like this for all other territories," Ukrainian Interior Ministry adviser Anton Herashchenko said.

Russian forces have suffered higher than expected losses in the first 10 days of fighting, which the Kremlin has tried to portray to its citizens as a "special operation" while banning Russian media from calling it a "war" or an "invasion."

Russia was slow to acknowledge that its forces had suffered major battlefield losses -- which earlier this week it listed at just under 500 dead while Ukraine has said Russia has lost more than 10,000 troops -- and has tried to justify its military action by questioning Ukraine's universally acknowledged status as a sovereign state.

In a televised appearance on March 5, Putin said that if Ukraine's leaders "continue to do what they are doing, they are calling into question the future of Ukrainian statehood."

WATCH: Video posted online showed a Russian jet being shot down near Chernihiv, northern Ukraine, on March 5. Later images showed the capture of the pilot, who ejected from his plane but was injured.

Ukraine Shoots Down Russian Jet, Captures Pilot

Russia's war in Ukraine has also attracted attention to Ukraine's northern neighbor, Belarus, whose embattled leader Alyaksandr Lukashenka has aided Moscow's military action

Belarus allowed thousands of Russian troops to stage the invasion from near its border with Ukraine, prompting further sanctions against the regime of Alyaksandr Lukashenka atop punitive measures already levied since a crackdown on a flawed presidential election in 2020.

On March 5, Russian media said the Russian and Belarusian foreign ministers had discussed setting up humanitarian corridors for "foreigners" leaving Ukraine. Details were unclear.

Mariupol is a strategically important city of more than 400,000 people on the Sea of Azov where water and power have been cut off for days.

The mayor of Mariupol, Vadym Boychenko, appeared to say via Telegram that the break would "give an opportunity to begin the restoration of critical infrastructure -- electricity, water, and mobile communications. It will also be possible to provide Mariupol with essential food and medicine."

"We are simply being destroyed," Boychenko said.

Volnovakha is a town of around 20,000 people that lies close to the former "line of contact" between Moscow-backed separatists and Ukrainian-controlled territory in the eight-year war that began shortly after Russia annexed Crimea in 2014.

Ukrainian and international accusations of possible war crimes and the targeting of civilians have mounted in recent days as images of blown-up Ukrainian apartment buildings and other residential areas have spread and local officials have warned of cutoffs of electricity and water.

WATCH: Zaporizhzhya has so far been spared attack, but Russian forces are moving north. As air sirens sounded, defiant local residents said that tension was ever-present.

'We'll Tear You Apart': A Mood Of Defiance In Ukrainian City

Shelling was continuing on March 5 in and around the capital, Kyiv, home to nearly 3 million people before the full-scale Russian invasion.

The Ukrainian military has warned that invading Russian forces are fighting to surround Kyiv and the besieged second city of Kharkiv in the east, as Western diplomats seek measures to curb the conflict and warn that civilians are likely to come under more intense attack.

Meanwhile, Zelenskiy confirmed in a video message posted early on March 5 that he and senior officials remain in Kyiv where "We continue to fight. We will protect our state. We will liberate our land."

But Zelenskiy reacted bitterly to NATO's rejection of pleas to impose a no-fly zone over non-member Ukraine.

"All the people who die from this day forward will also die because of you, because of your weakness, because of your lack of unity," he said in his overnight address "The alliance has given the green light to the bombing of Ukrainian cities and villages by refusing to create a no-fly zone."

The Ukrainian military said in a report early on March 5, the 10th day of the invasion, that Russian forces were using aerial support and high-precision weapons in their assault.

Ukraine's military said on March 5 that Russian soldiers were trying to expand their captured territory to the administrative borders of the eastern Luhansk and Donbas regions, where the separatists have been fighting an eight-year war against the central government.

The Ukrainian command said Kyiv continued to fight off the "enemy offensive."

SEE ALSO: Snapshots From The War: Under Heavy Fire Or Tensely Waiting, All Ukraine Is Under Siege

Tens of thousands of residents were crowding Kyiv's main train station as mostly women and children tried to flee the threat of encirclement and bombardment.

Western intelligence officials believe Russia is poised to try to "bombard cities into submission," according to CNN.

The UN has estimated at least 331 civilian deaths, although a lack of access to many besieged areas means that could be an undercount. Ukrainian authorities say at least 2,000 civilians have died.

The UN refugee agency said more than 1.2 million people had fled Ukraine since the launch of the war on February 24. More than half of those war refugees have gone to Poland.

In Russia, authorities have intensified their crackdown on domestic and international media.

Traditional and social media have been blocked or prevented from news-gathering and reporting by moves that have affected major international news providers like BBC, CNN, and RFE/RL, as well as Facebook, YouTube, and Twitter.

SEE ALSO: Russian Media Watchdog Blocks Facebook After Limiting Access To Multiple Other Sites

CNN cited "indications" that Russian mercenaries could already be fighting "in some places." It quoted an unnamed U.S. official as saying Russia appears to be planning to deploy up to 1,000 more mercenaries soon.

Meanwhile Ukrainian workers continue to operate a nuclear power plant at Zaporizhzhya where a building caught fire under Russian bombardment a day earlier "at gunpoint," according to energy officials.

WATCH: Staff at Ukrainian nuclear sites, Zaporizhzhya and Chernobyl, are being held by Russian forces and working under the barrel of a gun, according to the former head of Ukraine's nuclear inspectorate.

Ukrainian Nuclear Plant Staff 'Being Held,' Says Atomic Safety Expert

Moscow has said a third round of cease-fire talks with Ukrainian officials is planned this weekend, but no time or site has been confirmed.

With reporting by AP, dpa, AFP, Reuters, CNN, BBC, and RFE/RL's Russian and Ukrainian services