"We agree on the need to maintain strong sanctions against Russia until it ends its aggression in Ukraine and on the need to support Ukraine as it implements important economic and democratic reforms," Obama said during a joint press conference with British Prime Minister David Cameron.
Western powers have slapped stringent sanctions on Russia for its actions in eastern Ukraine last year which effectively led to the annexation of Crimea.
Obama has said the sanctions have worked, weakening President Vladimir Putin.
The ruble has slumped by 40 per cent this year, mostly due to crude oil prices falling by half in the past six months.