Obama said he would consult key European leaders later Friday over the current crisis on Ukraine, as Merkel phoned Russian President Vladimir Putin to voice her "great concern" over the standoff.

US President Barack Obama said he would consult key European leaders later Friday over the current crisis on Ukraine, as German Chancellor Angela Merkel phoned Russian President Vladimir Putin to voice her "great concern" over the standoff.

Obama said in Seoul that he wanted to coordinate a united approach with Western US allies, after Washington concluded that Russia ‘had done nothing’ to implement the deal reached in Geneva.

"I will be talking to the Europeans, not all of them, but some key European leaders again this evening, making sure they share my assessment in terms of what has happened since the Geneva talks," Obama told a press conference.

The president said Washington had already lined up further targeted sanctions against Russia "that are ready to go".

For her part, Merkel “expressed her great concern over the tense situation in eastern Ukraine and said she expects Russia's government to express its commitment to the Geneva agreement and to cooperate in its implementation," her spokesman Steffen Seibert said.

"Russia should publicly declare that it fully supports the Geneva declaration and it should publicly call on the armed pro-Russian groups in Ukraine to refrain from violence and lay down their arms," Seibert said.

He said that so far Russia's position since the Geneva deal had been "absolutely disappointing" and "we can see no progress whatsoever".

Ukraine, Russia, the European Union and the United States last week signed a deal in Geneva aimed at easing tensions in eastern Ukraine, where pro-Russian gunmen have occupied government buildings.