The United States has repeated its warning that the United Kingdom must not leave the European Union, following David Cameron’s announcement he wants to hold a referendum.

President Obama’s press secretary Jay Carney said on Wednesday the White House believed the UK was “stronger” as a member of the EU.

“We welcome the prime minister’s call for Britain to remain in the EU and to retain a leading role in Europe’s institutions,” he said.

“And as the President told the prime minister when they spoke last week, the United States values a strong United Kingdom and a strong European Union.

“We value our essential relationship with the UK., as well as our relationship with the European Union, which makes critical contributions to peace, prosperity, and security in Europe and around the world.

“We believe that the United Kingdom is stronger as a result of its European Union membership, and we believe the European Union is stronger as a result of having the United Kingdom in the EU.”

He added: “So that's - our views on this are very clear.”

On Wednesday Tory MPs hailed Cameron’s historic announcement that if he won a majority in 2015 he would hold an in or out referendum on Britain’s membership of the EU.

Earlier this month, before Cameron delivered his speech, US assistant secretary of state for European affairs Phil Gordon warned Britain against turning “inwards” with a referendum.

"We have a growing relationship with the EU as an institution, which has an increasing voice in the world, and we want to see a strong British voice in that EU,” he told journalists during a London briefing.

“That is in America's interests. We welcome an outward-looking EU with Britain in it."

President Obama repeated the sentiment during a phone call with the prime minister last week.

In a statement following the call the White House said: "The president underscored our close alliance with the United Kingdom and said that the United States values a strong UK in a strong European Union, which makes critical contributions to peace, prosperity, and security in Europe and around the world.”

Asked about British plans for an EU referendum during Wednesday’s daily press briefing, Carney said: “The internal processes by which these matters are considered within the UK or any other country are obviously the province of those countries and those governments.”

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