United States officials said on Monday that Treasury Secretary Janet Yellen would skip some meetings of finance ministers from the G20 - a group of advanced and emerging economies - if Russian officials were present.

Sunak, Britain's chancellor of the exchequer, will not attend all G20 meetings either, a government source said.

"As per the U.S., the chancellor will attend the core G20 sessions ... and will continue working with our allies to call out Russian aggression, and push for stronger coordinated action to punish Russia and support Ukraine," the source said.

Britain and other Western countries have imposed wide-ranging sanctions on Russian oligarchs, politicians and military officials, as well as targeting banks, defence companies and other firms.

Last week Britain froze $10 billion of assets belonging to two close associates of Chelsea Football Club owner Roman Abramovich, in what the government said was its largest ever asset freeze, and on Tuesday it homed in on the Moscow stock exchange.

Russia's finance minister, Anton Siluanov, said on Tuesday that he would lead Russia's delegation to the G20 sessions, which take place on the sidelines of twice-yearly meetings of the International Monetary Fund and World Bank.

Russia says its actions in Ukraine are a special operation to demilitarise its neighbour.