David Cameron is hoping to send a tough message on Ukraine from the leaders of the West's largest powers as the G7 summit in Germany concludes today.
The Prime Minister last night held talks with US president Barack Obama at which both agreed the need to maintain harsh sanctions against Russia until Moscow shows it has fully implemented last year's Minsk peace agreement.
US President Barack Obama has said that America is "looking forward" to the United Kingdom remaining part of the European Union.
Mr Obama's comments came as he met Prime Minister David Cameron for talks in the margins of the G7 summit of world leaders in Schloss Elmau, Germany.
They are the strongest indication yet that Washington wants a Yes vote in the referendum which Mr Cameron has promised by the end of 2017 on whether Britain should stay in the EU.
Greeting Mr Cameron at the start of the bilateral talks, Mr Obama said the US-UK relationship remains strong, telling reporters: "We have no closer partner around the world on a whole host of issues."
And he added: "I would note that one of the great values of having the United Kingdom in the European Union is its leadership and strength on a whole host of global challenges, so we very much are looking forward to the United Kingdom staying part of the European Union because we think its influence is positive not just for Europe, but also for the world."
Barack Obama has urged David Cameron to keep meeting the Nato target of spending 2% of GDP on defence.
David Cameron will use the G7 summit in Germany to call for an international effort to clean up governments and businesses around the world.