The United Nations Security Council has held an emergency meeting following Russia's attack on Europe's biggest nuclear power plant in south-eastern Ukraine.
Russian invasion forces seized the Zaporizhzhya nuclear power plant in heavy fighting, triggering global alarm. However a huge blaze in a training building at the site has been extinguished and officials say the facility is now safe.
US representative Linda Thomas-Greenfield told the meeting Russia's actions were "reckless" and "dangerous".
"By the grace of God, the world narrowly averted a nuclear catastrophe last night," she said.
"We all waited to exhale as we watched the horrific situation unfold in real time."
With Russian forces 32 kilometres away from another nuclear facility, she warned there was still "imminent danger", and she demanded assurances from Moscow that such an assault would not happen again.
The US embassy in Kiev tweeted that the attack amounted to a "war crime".
"It is a war crime to attack a nuclear power plant," the post read.
"Putin's shelling of Europe's largest nuclear plant takes his reign of terror one step further."
The US State Department sent a message to all its embassies in Europe telling them not to retweet the Kyiv embassy's tweet, according to CNN, which said it reviewed the message.
US Pentagon spokesman John Kirby condemned the attack at a press conference, saying nuclear power plants are "not designed to withstand combat".
"Attacking a nuclear power plant is exceedingly dangerous and could have visited a lot more damage and destruction to the people of Ukraine, and perhaps even to neighbouring countries, had this gone a different way."
Combat raged elsewhere in Ukraine as Russian forces surrounded several cities in the second week of the assault launched by Russian President Vladimir Putin.
A presidential advisor said an advance had been halted on the southern city of Mykolayiv after local authorities said Russian troops had entered it.
If captured, the city of 500,000 people would be the biggest yet to fall.
The capital, Kyiv, in the path of a huge Russian armoured column that has been stalled on a road for days, came under renewed attack, with air raid sirens blaring in the morning and explosions audible from the city centre.
Second nuclear power plant seized
Although the power plant was now said to be safe and the fire out, officials remained worried about the precarious circumstances, with Ukrainian staff operating under Russian control.
International Atomic Energy Agency chief Raphael Grossi described the situation as "normal operations, but in fact there is nothing normal about this".
He paid homage to the plant's Ukrainian staff: "to their bravery, to their courage, to their resilience because they are doing this in very difficult circumstances."
Mr Grossi said the plant was undamaged from what he believed was a Russian projectile and that only one reactor was working, at around 60 per cent of capacity. He was trying to contact Russian and Ukrainian officials to sort out political responsibility.
An official at Energoatom, the Ukrainian state nuclear plant operator, said there was no further fighting and radiation was normal, but his organisation no longer had contact with the plant's management or control over potentially dangerous nuclear material.
"Personnel are on their working places providing normal operation of the station," the official said.
Russia's defence ministry also said the plant was working normally. It blamed the fire on a "monstrous attack" by Ukrainian saboteurs and said its forces were in control.
Russian advance stalled by fierce resistance
Russia's grip on a plant that provides more than a fifth of Ukraine's electricity was a big development after nine days of war in which other Russian advances have been stalled by fierce resistance.
A Russian air strike on a rural residential area in Kyiv region killed at least seven people on Friday, including two children, Ukraine state police said in a statement.
Police said the strike hit the village of Markhalivka, around 10 kilometres from the south-western outskirts of the capital.
In Kyiv's Borshchahivka neighbourhood, the twisted engine of a cruise missile lay in the street where it had apparently been downed overnight by Ukrainian air defences.
Residents were furious but also proud of what they see as the successful defence of the city of 3 million, which Russia had hoped to capture within days.
Russian troops "all should go to hell," said Igor Leonidovich, 62, an ethnic Russian who had moved to Ukraine 50 years ago as a boy.
Russian forces continue to advance from three directions, pounding cities with artillery and air strikes.
Only one sizeable Ukrainian city, the southern port of Kherson, has fallen to Russian forces since the invasion began.
Russian forces were driven out of the Ukrainian city of Mykolayiv after attacking it on Friday but fighting continued around the city outskirts, regional governor Vitaliy Kim said.
Earlier, Mykolayiv's mayor said Russian forces had reached inside his city, a shipbuilding port of 500,000 people.
Mr Zelenskyy's military adviser, Oleksiy Arestovych, said the Russian advance there had been halted.
The south-eastern port of Mariupol has been encircled and bombarded, Britain said in an intelligence update. Authorities there have described a humanitarian emergency.
The mayor of Mariupol said on Friday the city had no water, heat or electricity and is running out of food after coming under attack by Russian forces for the past five days.
Mayor Vadym Boychenko made a televised appeal for military help and said a humanitarian corridor should be created to evacuate civilians from the port city.
Ukrainian troops are holding the line against the attempted Russian advance on Mariupol, but need significant back-up, said a deputy commander of the Azov military unit, part of Ukraine's National Guard.
"This is the last city that prevents the creation of a land corridor from Russia to Crimea," he said in a post on Azov's official Telegram page, identifying himself by his call sign Kalyna.
"Mariupol cannot be lost."
Ukrainian artillery have been defending the Black Sea port city of Odesa from repeated attempts by Russian ships, Mr Arestovych said, insisting there was no immediate threat to the city.
In the north-east, along another axis of the Russian attack, Kharkiv and Chernihiv have been under bombardment since the start of the invasion. Strikes have intensified but defenders are holding out.
A Russian air strike on Thursday also destroyed the power plant in Okhtyrka, leaving the small city 100km north-west of Kharkiv without heat or electricity, the head of the region said.
As US defence official said on Friday that Ukraine still has a "significant majority" of its military aircraft available nine days after Russian forces started their invasion of the country.
"The Ukrainians still have a significant majority of their air combat power available to them, both fixed wing and rotary wing as well as unmanned systems and surface to air systems," the official said, speaking on the condition of anonymity.
Critics of war face 15 years jail in Russia
On Friday, Mr Putin formally signed a law that would impose a jail term of up to 15 years for people who intentionally spread "fake" information about Russia's armed forces, TASS news agency reported.
The law was drafted earlier in the day by Russia's upper house of parliament.
Mr Putin also signed a law that would mean those who called for sanctions against Russia would be held criminally responsible, the news outlet said.
Ukrainian President Volodymyr Zelenskyy continued to call for worldwide support in an effort to stop the Russian invasion.
"Europeans, please wake up. Tell your politicians – Russian troops are shooting at a nuclear power plant in Ukraine," Mr Zelenskyy said in a video address. In another address, he called on Russians to protest.
Jailed Kremlin critic Alexei Navalny on Friday told Russians to protest against the war in Ukraine in Russian cities and across the world on March 6, and accused Mr Putin of bringing shame on the Russian national flag and language.
"Show the world that Russians don't want war. Come out in the squares of Berlin, New York, Amsterdam or Melbourne, wherever you are," Mr Navalny said in a blog post.
"Now we are all responsible for Russia's future. For what Russia will be in the eyes of the world."
The Russian invasion of Ukraine has led to a further crackdown of dissent in the former Soviet nation, with the lower house of parliament introducing legislation on Friday to impose jail terms on people who spread "fake" reports about the military.
With Russians now facing hefty prison sentences for spreading information that is not in line with Moscow's position on the war in Ukraine, authorities have also blocked access to foreign media outlets in the country.
On Friday, Russia shut down foreign broadcasters including the BBC and Voice of America, following the shuttering of prominent independent Russian broadcasters TV Dozhd (Rain) and Ekho Moskvy radio on Thursday.
The BBC announced they will temporarily suspend the work of journalists in the country so as not to expose staff to possible criminal prosecution.
The news service would continue to operate from outside of Russia, they added.
Civilian deaths continue to rise
Thousands of people are believed to have been killed or wounded and more than 1 million refugees have fled Ukraine since February 24, when Mr Putin ordered the biggest attack on a European state since World War II.
The UN human rights office said on Friday it had confirmed 331 civilians have been killed and 675 injured in Ukraine since Russia's invasion began on February 24, adding that the real toll was likely much higher.
The toll, through to midnight on Thursday, rose from 249 in its previous report from a day earlier. Among the 331 killed were 19 children, the UN rights office said.
Most of the victims were killed by explosive weapons such as shelling from heavy artillery, multi-launch rocket systems and missile and air strikes, according to the rights office, which has monitors in Ukraine.
The UN’s top human rights body on Friday voted overwhelmingly to appoint a three-person panel of experts to monitor human rights in Ukraine.
ABC/wires
