Putin has no idea what's coming: Biden

Washington: US President Joe Biden warned Vladimir Putin that the Russian leader "has no idea what's coming", as Western nations tightened an economic noose around Russia, whose invading forces bombarded Ukrainian cities and appeared poised for an advance on Kyiv.

Hundreds of thousands of Ukrainians have fled the fighting since Putin ordered a full-scale invasion nearly a week ago, with a miles-long Russian military convoy north of Kyiv readying to advance on the capital.

Russian forces had taken control of Kherson, a city of nearly a quarter million people just north of Crimea, the peninsula annexed by Russia in 2014, a Russian defence ministry spokesperson said.

"While he may make gains on the battlefield- he will pay a continuing high price over the long run," Biden said in his State of the Union address. Straying from the prepared text, Biden added "He has no idea what's coming." He did not elaborate.

US lawmakers stood, applauded and roared, many of them waving Ukrainian flags and wearing the country's blue and yellow colours, as Biden delivered his address to the chamber of the House of Representatives.

A senior US defense official said on Tuesday the invading force's advance on Kyiv has stalled due to logistics problems, including shortages of food and fuel, and some units appeared to have low morale.

Ukrainian President Volodymyr Zelenskiy called on Russia to stop bombarding civilians and resume talks.

"It's necessary to at least stop bombing people, just stop the bombing and then sit down at the negotiating table," he told Reuters and CNN in a joint interview in a heavily guarded government compound in Kyiv.

More than 450,000 people have fled Ukraine to Poland, and a further 113,000 to Romania.