US secretary of state Antony Blinken said Washington was in “very active discussions” with its European partners about a ban on oil imports from Russia, as Ukraine braced for a widening offensive against its urban centres.

Restrictions on Russian oil would be a big step up in the west’s response to Moscow over its invasion of Ukraine with potentially serious ramifications for the global economy. It would also mark an about-turn by the White House, which had rejected bipartisan calls to ban Russian oil imports to the US, saying an embargo would limit global supply and raise prices for consumers.

The move would further isolate Russia’s economy, which is already reeling under heavy sanctions and a growing corporate boycott. This weekend, payment networks Mastercard, Visa and American Express, accountants PwC, streaming service Netflix and social video app TikTok added their names to a long list of companies withdrawing operations from Russia.