US President Barack Obama has said that America is "looking forward" to the United Kingdom remaining part of the European Union.
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."
Obama's comments come on the same day as Labour leadership contender Liz Kendall criticised the Prime Minister for reducing the question of Britain's future relationship with the EU to the issue of migration.
The shadow health minister accused David Cameron of putting "internal political management" before the national interest.
She described the policy of removing tax credits to migrant workers as "definitely something we should look at" but called for a wider debate on the subject ahead of the referendum in 2017.
Ms Kendall told BBC 1's The Andrew Marr Show: "We do have to deal with the issue of people who come here to work. They must be working and not claiming benefits. But this is about something much bigger - it is about the future of our country and our place in the world.
"David Cameron should be focusing on what is in Britain's national interest and our place in the world, not on internal party politics."
Asked if she was in favour of removing tax credits to migrant workers, she replied: "That's definitely something we should look at, but this is a far bigger debate.
"Of course David Cameron is reducing the question because he has failed to show leadership with his own backbenchers.
"He has allowed this to define whether or not Britain remains part of Europe. That is a profound lack of leadership on his behalf because he is more concerned about internal political management than the future of the country."
Pushed on the migration question again, she added: "I'm in favour of free movement of labour but not free movement of benefits. People who come here should come here to work.
"If we allow this debate to be defined by that issue alone, we will be profoundly wrong. This about Britain's place in the world, our future economy."
She reiterated her support for maintaining the 2% defence spending commitment, adding: "Our place in Europe is essential as part of our wider international relationship."
Asked about the need to cut the deficit, she said: "Let's see what the Conservatives come out with in their budget. I'm not going to provide a budget response to a budget that has not been delivered."