Obama: European unity not in crisis, but under strain

President Barack Obama said Friday that European unity is under strain and insisted that Britain should remain in the European Union.

Obama made his comments standing next to U.K. Prime Minister David Cameron at 10 Downing St. in London. Cameron has been fighting to defeat a June 23 referendum that proposes that Britain leave the EU.

"I wouldn't describe European unity as in a crisis, but I would say it's under strain. Some of that has to do with the aftermath of the financial crisis and the strains that we're all aware of with respect to the euro zone," Obama said.

The president encouraged continued collaboration between Britain and the United States, while also arguing for Cameron that Britain should remain in the EU.

"I think it's important to emphasize as David points out that the U.K. is not part of the euro zone, so the blowback to the British economy has been different than on the continent," Obama added.

Obama's visit comes two months before the so-called Brexit vote. He's been criticized by advocates of the exit for injecting himself into the domestic British debate.

U.K. Independence Party leader Nigel Farage said Obama should "butt out." And London Mayor Boris Johnson, a leader of the exit campaign, said Americans "would never contemplate anything like the EU for themselves."

Writing in The Sun newspaper, Johnson said Obama's stance "is a breathtaking example of the principle of do as I say, not as I do."

At the news conference, Obama defended his right to offer his opinion.

"In democracies, everybody should want more information than less. You shouldn't be afraid to hear an argument being made. That's not a threat. That should enhance the debate," he said.

In op-ed published Friday in the Daily Telegraph, Obama said that "a strong Europe is not a threat to Britain's global leadership; it enhances Britain's global leadership."

"Let me be clear, ultimately this is something the British voters have to decide for themselves," Obama told reporters at the news conference. "But as part of our special relationship, part of being friends is to be honest and to let you know what I think. Speaking honestly the outcome of that decision is a matter of deep interest to the United States because it affects our prospects as well."

— The Associated Press contributed to this report.