Obama wades in to UK's Brexit debate

US President Barack Obama plunged into Britain's poisonous European Union membership debate Friday, arguing strongly against a "Brexit" as he kicked off a visit to the UK.

Obama's intervention ahead of the June 23 vote in a piece for the Daily Telegraph newspaper drew a furious response from eurosceptics like London Mayor Boris Johnson, who said he should mind his own business.

Writing in the Telegraph, a traditional bastion of euroscepticism, Obama argued that Britain's place in the EU magnifies its global influence and its membership is a matter of "deep interest" to the United States.

Noting that he wanted to mark the 90th birthday of Queen Elizabeth II on Thursday in person, he and First Lady Michelle Obama will at lunch at Windsor Castle later Friday the president was also unusually forthright about his country's interest in Britain's EU membership.

Stressing that the choice was purely for the British people, he wrote: "I will say, with the candour of a friend, that the outcome of your decision is a matter of deep interest to the United States.