(QHA) -

U.S. President Barack Obama has urged Moscow to engage with Ukraine's President-elect Petro Poroshenko. 

Obama spoke after talks with British Prime Minister David Cameron on June 5 in Brussels.

He said Poroshenko's inauguration presents an opportunity which Russia needs to seize. 

At a summit in Brussels, leaders of the Group of Seven leading industrialized nations warned President Vladimir Putin that he "must stop" Russia's "destabilizing" actions in Ukraine or face further sanctions. 

At the close of the summit, European Commission President Jose Manuel Barroso said: "The G7 stands united behind Ukraine, politically and economically." 

"The G7 leaders will convey this message" to Putin on the sidelines of D-Day commemorations in France on June 6, he added.