LONDON - US President Barack Obama wasted no time in plunging into Britain's poisonous EU membership debate Friday, arguing strongly against a "Brexit" as he kicked off a visit to the UK.
Obama went to a traditional bastion of euroscepticism, The Daily Telegraph newspaper, to make the case that Britons should vote to remain in the European Union in the June 23 referendum.
Writing in the broadsheet, 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.
"I realise that there's been considerable speculation - and some controversy - about the timing of my visit," Obama wrote.
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 candor of a friend, that the outcome of your decision is a matter of deep interest to the United States.
"The path you choose now will echo in the prospects of today's generation of Americans." Polls put the pro-EU and Brexit camps neck-and-neck among those who express a preference to vote.
Obama's intervention is an unusual overt foray into the domestic politics of another country.
Seen from Washington, Prime Minister David Cameron's decision to call a referendum was a bold - if not downright risky - gamble that could leave Britain and the EU badly weakened.
"The EU has helped spread British values and practices - democracy, the rule of law, open markets - across the continent and to its periphery," Obama wrote.
"The European Union doesn't moderate British influence - it magnifies it.
"A strong Europe is not a threat to Britain's global leadership; it enhances Britain's global leadership," he said.
Britain's voice in the EU keeps the bloc "outward looking" and "closely linked" to the United States, he said.
"The US and the world need your outsized influence to continue - including within Europe." For many Atlanticists in the anti-EU camp, Obama's argument against Brexit and in favour the "special relationship" may prove a powerful one.
Obama will likely be asked to weigh in further during a joint press conference with Cameron following talks at his Downing Street office later Friday.
Pro-Brexit supporters issued pre-emptive calls for the US president to stay out of the EU referendum debate and cast him as a meddling outsider.
Nigel Farage, leader of the anti-EU UK Independence Party, said Obama should "butt out", while former cabinet minister Iain Duncan Smith said he failed to see how an intervention by the US leader could be "appropriate".
That argument could also be a potent one in a country that shares cultural affinities with the United States, but which is deeply wary of being treated as Washington's lapdog.
More than 100 lawmakers have reportedly written to the US ambassador in London to make their displeasure known.
Cameron, in the political fight of his life, has tried to stress that close ties with the United States will endure.
He sought to underscore areas of continued cooperation by saying his talks with Obama would focus heavily on the fight against the Islamic State jihadist group.
"Britain's relationship with the United States is special and enduring. Based on shared values and convictions it has stood the test of time," Cameron said in a statement.
"I am deeply proud of what it has allowed us to achieve, in dealing with the global challenges we both face.
"I am confident that Britain and the US can continue to build on a solid basis of friendship and a shared commitment to freedom, democracy and enterprise to shape a better world for future generations." During Obama's visit he and the first lady will dine Friday with Queen Elizabeth's grandson Prince William, his wife Kate and his brother Prince Harry.
From Britain he will travel to Germany for a meeting with German Chancellor Angela Merkel and other EU leaders.