New sanctions could be imposed on Russia if it does not take additional steps to resolve the Ukrainian conflict, White House press secretary Josh Earnest has said.

"As long as they [the Russians] fail to contribute in a substantive way to de-escalate in that conflict they are only increasing the risk that the international community will impose further costs and further isolate Russia," he said at a briefing on Monday, adding that Washington and Brussels are trying to show Moscow that it would have to answer if it does not change its attitude towards Ukraine.

Earnest recalled that the United States and the EU were calling on Russia to withdraw its troops from the border with Ukraine, ensure the cessation of arms supplies to militants and persuade them to lay down their arms.

He said that there is evidence that Russia is not doing enough to stop illegal arms shipments to eastern Ukraine.