America and the world need a united and strong Europe, warns Obama.
US PRESIDENT Barack Obama has delivered an impassioned defence of the European Union, warning that America and the world need a "united" Europe.
In comments which are likely be seen as a further plea for a Remain vote in Britain's June 23 referendum, Mr Obama hailed the EU as "one of the greatest political and economic achievements of modern times" and cautioned individual states against rebuilding barriers which existed in the 20th century.
Mr Obama's intervention, in a speech in Germany, came as Brexit's biggest hitters sought to seize back the referendum initiative by putting immigration at the top of the agenda.
Justice Secretary Michael Gove warned that the UK faces a migration "free-for-all" unless it breaks away from Brussels as the Leave camp moved to exploit an admission from the Government that EU free movement of labour rules make it harder to curb immigration.
But the US president warned of the dangers of an "increasing intolerance" in politics which promoted an "us versus them" mentality towards migrants.
Speaking at the start of the G5 summit in Hanover, where he will discuss security threats with David Cameron, Chancellor Angela Merkel, French president Francois Hollande and Italian PM Matteo Renzi, Mr Obama acknowledged that anxieties over globalisation, terrorism and immigration were "real and legitimate".
"All these challenges have led some to question whether European integration can long endure, whether you might be better off separating off, redrawing some of the barriers and the walls between nations that existed in the 20th century," said the US president But he added: "If a unified, peaceful, liberal, pluralistic, freemarket Europe begins to doubt itself, begins to question the progress that's been made over the last several decades, then we can't expect the progress that is just now taking hold in many places around the world will continue.
"Instead, we will be empowering those who argue that democracy can't work, that intolerance and tribalism and organising ourselves along ethnic lines and authoritarianism and restrictions on the press - that those are the things that the challenges of today demand.
"I've come here today to the heart of Europe to say that the United States and the entire world needs a strong and prosperous and united Europe."
President Obama said he understood that dealing with Brussels could be "frustrating" and slow down decision-making.
But he said the union had brought peace among its members and insisted that a strong, united Europe was vital for global security and prosperity.
He said: "European unity can require frustrating compromise. It adds layers of government that can slow decision-making.
"I understand. I have been in meetings with the European Commission.
"And, as an American, we are famously disdainful of government. We understand how easy it must be to vent at Brussels and complain.
"But, remember that every member of your union is a democracy. That's not an accident.
"Remember that no EU country has raised arms against another. That's not an accident."
President Obama said a "strong united" Europe remains a "necessity for all of us".
"It's a necessity for the United States because Europe's security and prosperity is inherently indivisible from our own," he added. "A strong united Europe is a necessity for the world because an integrated Europe remains vital to our international order."
President Obama said Islamic State was the "most urgent threat" to Western nations and warned the EU it "could do more" through air strikes, military trainers and economic assistance to stabilise Iraq. Urging all EU countries to meet the Nato target of spending 2% of national income on defence, he added: "Sometimes Europe has been complacent its own defence."
Boris Johnson came out fighting after being widely condemned over his highly personalised attacks on Mr Obama during the president's two-day visit to the UK.
And former Cabinet minister Iain Duncan Smith said Mr Obama was wrong to suggest that the UK would be at the "back of the queue" for a trade deal, claiming there were many politicians in Washington eager for an agreement with post-Brexit Britain.
The London mayor turned his fire on Prime Minister David Cameron with a scathing assault accusing him of achieving "two-thirds of diddly squat" in negotiations with Brussels for a special deal for Britain on immigration and other key demands.
But he sidestepped questions about the row he caused by referring to President Obama's "part-Kenyan" heritage.
Asked about accusations of "dog-whistle racism", Mr Johnson told Sky News: "Look, I think the crucial thing is what kind of future is there for this country outside the EU.
"We've been told we have to go to the back of the queue. That seems to me to be ridiculous when you consider the real reason we haven't been able to do a free trade deal with the United States in the last 43 years is we are part of the EU."
In his Daily Telegraph column, Mr Johnson warned the Remain side not to "crow too soon" that the Leave side had been "bombed into submission".
"The Prime Minister asked the EU for reform and got two-thirds of diddly squat. That deal shows how contemptuously we will be treated if we remain," Mr Johnson said.
Mr Duncan Smith backed Mr Johnson over his attack on Mr Obama, although acknowledged it may have been "clumsy".
"He simply referred to some of the reasons why he may have a particular lack of regard for the UK," the former work and pensions secretary told BBC Radio 4's Today programme.
Mr Duncan Smith said he had been "surprised" to see the president of the USA "lecturing the UK, British citizens, as to what they should do in the forthcoming referendum."
And he challenged Mr Obama's suggestion that it could take 10 years for the UK to seal a free trade agreement with the US, insisting that "nobody knows" how long it takes for such deals to be completed.
Mr Gove insisted potential new members of the EU such as Turkey and Albania posed a "direct and serious threat" to public services such as the NHS, and social harmony.
The Cabinet heavyweight wrote in The Times that the health service faced "unquantifiable strain" unless Britain quits the EU.
Downing Street rejected Mr Gove's comments regarding the threat posed by the possible accession to the EU of Turkey and Albania.
The Prime Minister's official spokeswoman said any discussions were "years away" and that the UK had a veto over any future enlargement.
"The Prime Minister negotiated, as part of the reforms that we secured in February, that for future accessions there will need to be a different set of transitional arrangements," the spokeswoman said. "So those out there talking about future countries joining seem to be looking at the past and not looking at the special status in the deal the Prime Minister has secured."
Former Cabinet minister and EU commissioner Lord Mandelson said the Vote Leave campaign had "hoisted the white flag on arguments around the economy" and were now running a "Ukiplite strategy centred on immigration".
<BDavid Cameron with Barack Obama yesterday
Barack Obama tests VR goggles when touring the Hanover Messe, the world's largest industrial technology trade fair, in Hannover, Germany, yesterday