Obama urges UK to stay in the European Union

He said the UK's EU membership "gives us much greater confidence about the strength of the transatlantic union".

Speaking to the BBC's North America editor Jon Sopel, he said the EU "made the world safer and more prosperous".

He also admitted that the failure to pass "common sense gun safety laws" in the US was his biggest frustration.

Mr Obama said the UK was America's "best partner" because of its willingness to project power beyond its "immediate self-interests to make this a more orderly, safer world".

He said British Prime Minister David Cameron had been an outstanding partner and congratulated his government for meeting the Nato target of spending 2% of GDP on defence. President Obama was speaking to the BBC at the White House before departing for Kenya, where he begins a short tour of Africa.

With just 18 months left in power, he said the area he has been "most frustrated and most stymied" in was gun control "even in the face of repeated mass killings".

"If you look at the number of Americans killed since 9/11 by terrorism, it's less than 100. If you look at the number that have been killed by gun violence, it's in the tens of thousands," Mr Obama said.

"For us not to be able to resolve that issue has been something that is distressing," he added.