Danylo Shapovalov, a surgeon volunteering for the Ukrainian territorial defence, said one of the Americans died instantly and he had treated the other.

Russia, the country he represents at the United Nations, had just invaded Ukraine, sending shock waves around the world that continue to reverberate today.

The service - part of the defence ministry - initially said the convoy left the village in a "green corridor" which had previously been agreed with Russia.

The Russian invasion - the biggest assault on a European state since World War Two - has upended Europe's security order and spurred EU capitals into rethinking what the bloc should stand for, its economic, defence and energy policies.

Biosecurity experts say Russia's movement of troops into Ukraine and bombardment of its cities have raised the risk of an escape of disease-causing pathogens, should any of those facilities be damaged.

At just 30 days from the first round of voting, the 44-year-old former investment banker has seen a spike in opinion polls since last week, garnering 30 percent of intentions to vote in several surveys.

"Three people were killed, including a female child, in yesterday's attack on a children's and maternity hospital in Ukraine's besieged Mariupol, according to updated figures this morning," the city council said on its Telegram channel. 

"The Kremlin is intentionally spreading outright lies that the United States and Ukraine are conducting chemical and biological weapons activities in Ukraine," State Department spokesman Ned Price said in a statement.

The plant "was fully disconnected from the power grid," Ukraine's energy operator Ukrenergo said in a statement on its Facebook page, adding that military operations meant "there is no possibility to restore the lines".

United Nations High Commissioner for Refugees Filippo Grandi told a news conference during a visit to Stockholm that "the time is now to try to help at the border", rather than discussions on the division of refugees between countries.

The trip was planned before Poland took the United States by surprise on Tuesday by offering to send its Mig-29 jets to Ukraine via a US air base.

On February 24, Russia invaded Ukraine and seized the defunct Chernobyl plant, site of a 1986 disaster that killed hundreds and spread radioactive contamination west across Europe.

There's no consensus on what the letter actually signifies, but almost two weeks into Russia's military incursion into Ukraine it has become synonymous with the Russian army.

The Vienna-based UN body said Ukrainian authorities reported an attack took place on Sunday, adding that no increase in radiation levels had been reported at the site.

The attack took place two days after Russia attacked the Zaporizhzhya Nuclear Power Plant, Europe's largest nuclear power station in southern Ukraine, having already captured the Chernobyl nuclear power complex in the north.

Amid tight security, Blinken and Kuleba held talks in a tent on the border where refugees, mostly women and children, were also crossing with their belongings in rolling luggage and backpacks.

"We know for sure that Ukrainian combat aircraft have flown to Romania and other neighbouring countries," defence ministry spokesman Igor Konashenkov said in a video briefing. 

According to Orange, nearly 9,000 subscribers of a satellite internet service provided by its subsidiary Nordnet in France are without internet following a "cyber event" on February 24 at Viasat, a US satellite operator of which it is a client. 

Ukrainian leader Volodymyr Zelensky has pleaded with the West to support a no-fly zone as his besieged country continues to resist Moscow's invasion, now in its second week. 

Moscow and Kyiv traded blame over a failed ceasefire plan that would have let civilians flee Mariupol and Volnovakha, two southern cities besieged by Russian forces. Another round of talks was tentatively planned for Monday as Ukrainians who could escape spilled into neighboring Poland, Romania, Slovakia and elsewhere.

Prime Minister Naftali Bennett's sit-down with Putin was the first by a foreign leader since the day Russian forces invaded Ukraine last week, and came after Kyiv had asked Israel to launch a dialogue with Moscow. 

Two members of security staff were injured when the projectile hit overnight after the Ukrainian authorities reported a battle with Russian troops near Europe's biggest power plant, which is operating at just a small fraction of its capacity with one of its six units still running.

The Ukrainian nuclear regulator said that the fire had been extinguished and no radiation leak had been detected, with site staff still able to work at the Zaporizhzhia site.

"No country other than Russia has ever fired on nuclear power units," he said in a video message released by his office. "This is the first time in our history. In the history of mankind. The terrorist state now resorted to nuclear terror."

"If it blows up, it will be 10 times larger than Chornobyl!" the minister said, referring to one of the world's worst nuclear disasters that occurred in 1986 at the Chernobyl plant in Ukraine, then part of the Soviet Union.

"IAEA Director General @RafaelMGrossi speaks with #Ukraine PM Denys Shmygal and with Ukrainian nuclear regulator and operator about serious situation at #Zaporizhzhia Nuclear Power Plant, appeals for halt of use of force and warns of severe danger if reactors hit," the International Atomic Energy Agency tweeted.

Indonesia's envoy to the United Nations said that the international community must go beyond condemnation and start “restoring trust and confidence”, as analysts predict the potential effects of the Ukraine crisis.

But the failures of the first days, including vastly underestimating the Ukrainians' willingness to fight back, could lead to a frustrated Moscow deciding to unleash all its power and indiscriminately destroying large swathes of Ukraine, they said.

Moscow's offensive marks a turning point for the whole world.

After more than two days of extraordinary debate, which saw the Ukrainian ambassador accuse Russia of genocide, 141 out of 193 United Nations member states voted for the non-binding resolution.