US President Barack Obama is in London on a four-day visit to Britain. Upon his arrival on Thursday night, Obama made an impassioned appeal for Britain to remain in the European Union.

People in the country will vote on the UK's membership of the 28-country bloc in a June 23rd referendum.

Obama said the referendum was a matter of deep interest to the US, and would affect the prospects of Americans too. He said Britain's place in the EU keeps the bloc closely linked to the United States and magnifies its voice in the world.

This is Obama's fifth visit to the country during his time in office. He's scheduled to have lunch today at Windsor Castle with Queen Elizabeth, who celebrated her 90th birthday on Thursday, and her husband Prince Philip. Obama is also scheduled to hold talks with Prime Minister David Cameron.