WASHINGTON: The White House is expected to impose a ban on U.S. imports of oil from Russia as punishment for the invasion of Ukraine, Democratic U.S. Senator Chris Coons said on Tuesday.

In an interview with CNN, Coons said the announcement of the ban could come on Tuesday or Wednesday. A source familiar with the plans told Reuters the announcement could come as soon as Tuesday.

Russia is the world's biggest exporter of oil and natural gas. It has been subjected to global financial sanctions over the war in Ukraine, but until now its energy exports were exempted.

Russia opened a humanitarian corridor on Tuesday letting Ukrainians flee the eastern city of Sumy, but Kyiv accused Moscow of shelling a similar route intended to allow residents to escape the besieged southern port of Mariupol.

"Ceasefire violated! Russian forces are now shelling the humanitarian corridor from Zaporizhzhia to Mariupol," Ukraine's foreign ministry spokesperson Oleg Nikolenko wrote on Twitter.

"8 trucks + 30 buses ready to deliver humanitarian aid to Mariupol and to evac civilians to Zaporizhzhia. Pressure on Russia MUST step up to make it uphold its commitments."

The United Nations said the number of refugees who have fled Ukraine had surged past 2 million, describing the flight as one of the fastest exoduses in modern times.

The economic impact of a conflict involving the world's top oil and gas exporter and two of its biggest grain and metals producers was also intensifying on Tuesday, fuelling concerns it could derail global recovery from the coronavirus pandemic.

U.S. gasoline pump prices hit a record high, London trade in industrial metal nickel had to be suspended after prices more than doubled in a matter of hours, and Britain's Shell said it was halting all purchases of Russian oil, apologising for buying a shipment last week.