A demonstrator holds placards and shouts at a rally to protest against Russia's invasion of Ukraine. AFP

His dramatic call for help came as Russian forces were approaching the Ukrainian capital, with some units reportedly reaching the city's northern suburbs.

"If you have combat experience in Europe and do not want to look at the indecision of politicians, you can come to our country and join us in defending Europe, where it is very necessary now," Zelensky, who appeared tired, said in a video.

Speaking on the second day of the attack launched by Russian President Vladimir Putin, Zelensky also asked Europeans to "demand from your governments that Ukraine receive more financial, more military aid."

The 44-year-old leader also said the West was in no hurry to help Ukraine against the Russian invasion. "How are you going to defend yourself when you are so slowly helping us in Ukraine?," he said. "State institutions in Europe are not in a hurry with really strong decisions."

Western countries have imposed sanctions on Moscow, but stopped short of cutting Russia off from the SWIFT international payments system.

Zelensky demanded that Europe go further and "act without delay." "Europe has enough strength to stop this aggression," he said.

"Cancellation of visas for Russians? Disconnect from SWIFT? Complete isolation of Russia? Recall of ambassadors? Oil embargo? Closing the sky? Today, all this must be on the table," he said.

Russian Foreign Minister Sergei Lavrov said Moscow was ready to talk but only if Ukraine's armed forces "lay down their arms", adding that "nobody intends to occupy Ukraine".

Russia has demanded that Ukraine to drop its ambition to join Nato and has called for the Western military alliance to scale back its presence in Eastern Europe.

'Left alone'

Zelensky said on Thursday there was now a "new iron curtain" between Russia and the rest of the world, adding later that his nation had been "left alone." "Who is ready to fight alongside us? I don't see anyone."

Among the highest-profile strategic developments on Thursday, Ukraine said Russian forces had seized the Chernobyl nuclear power plant — prompting concern from international nuclear watchdogs.

Ukrainian officials said on Friday that radiation levels had increased in the Chernobyl exclusion zone and warned the capture of the plant by Russian soldiers could have "terrible consequences."

Russia said Thursday it had destroyed more than 70 Ukrainian military targets, including 11 airfields. Western intelligence confirmed Moscow had established "complete air superiority" over Ukraine.

Agencies