According to the UK refugee agency, 1 million people have fled Ukraine since Russia’s invasion.

This is the fastest vacation of refugees in this century, Press Association has reported.

This number amounts to more than 2% of Ukraine’s population on the move in under a week.

The World Bank counted the population at 44 million at the end of 2020.

This comes as Russian forces lay siege to two strategic Ukrainian ports and press their bombardment of the country’s second-biggest city, while the huge armoured column threatening Kyiv appeared to be stalled outside the capital.

However, Moscow’s isolation has deepened while most of the world lined up against it at the United Nations to demand it withdraw from Ukraine.

The prosecutor for the International Criminal Court has opened an investigation into possible war crimes in Ukraine.

UNHCR, meanwhile, predicted up to 4 million people could eventually leave Ukraine but cautioned even that projection could be revised upward.

In an email, UNHCR spokesperson Joung-ah Ghedini-Williams wrote: “Our data indicates we passed the 1M mark” as of midnight in central Europe (11pm London), based on counts collected by national authorities.

UNHCR spokesperson Shabia Mantoo said Wednesday that “at this rate” the outflows from Ukraine could make it the source of “the biggest refugee crisis this century”.

Russia reported its military casualties for the first time since the invasion began last week, saying nearly 500 of its troops have been killed and almost 1,600 wounded.

Ukraine did not disclose its own military losses but said more than 2,000 civilians have died, a claim that could not be independently verified.

Russian President Vladimir Putin’s forces claimed to have taken complete control of Kherson, which would make it the biggest city to fall yet in the invasion.

But a senior US defence official disputed that.

“Our view is that Kherson is very much a contested city,” the official said.

But the mayor of Kherson, Igor Kolykhaev, said Russian soldiers were in the city and came to the city administration building.

He said he asked them not to shoot civilians and to allow crews to gather up the bodies from the streets.

“I simply asked them not to shoot at people,” he said in a statement.

“We don’t have any Ukrainian forces in the city, only civilians and people here who want to LIVE.”

Mariupol mayor Vadym Boychenko said the attacks there had been relentless.

“We cannot even take the wounded from the streets, from houses and apartments today, since the shelling does not stop,” he was quoted by the Interfax news agency as saying.