Europe and America today launched talks on a free trade deal which Prime Minister David Cameron believes could add £100 billion to the world economy.
The agreement came as leaders of the world's most powerful countries gathered in Northern Ireland for a G8 summit which was overshadowed by international tensions over the civil war in Syria.
Mr Cameron today spoke privately with Barack Obama - who has said he may arm the rebels seeking to oust the regime of Bashar Assad - ahead of the US president's talks with Russia's Vladimir Putin, Assad's most powerful international backer.
The dramatic gulf between Russia and the West over Syria was laid bare in talks between Mr Cameron and Mr Putin at Downing Street yesterday, when the Russian president warned the international community to be wary of arming militants who "eat the organs" of their enemies.
Mr Cameron said this morning he was "as worried as anyone" about terrorist and extremist elements in the opposition forces, but insisted it was right to engage with the Syrian crisis and seek to put pressure on both sides to attend peace talks to discuss a transitional government for the country.
But the Prime Minister was also fighting to keep the world's attentions focused on the economic priorities which he has set for the two-day G8 summit in Lough Erne, particularly the EU/US pact which he said would be "the biggest bilateral trade deal in history".
"The whole point of this meeting in Lough Erne is to fire up our economies and drive growth and prosperity around the world, to do things that make a real difference to people's lives," said the PM, in shirt sleeves and tieless after completing talks with Mr Obama and EU leaders.
"There is no more powerful way to do that than by boosting trade and there is no better way than by launching these negotiations on a landmark deal between the EU and the USA, a deal that could add as much as £100 billion to the EU economy, £80 billion to the US economy and as much as £85 billion to the rest of the world. They mean extra jobs, more choice and lower prices in our shops."
Mr Obama promised to make the trade talks, which start next month in Washington and are expected to last up to two years, a priority of his remaining term in office.
"America and Europe have done extraordinary things together before and I believe we can forge an economic alliance as strong as our diplomatic and security alliances, which of course have been the most powerful in history," he said.
The President made clear he expects a bumpy ride for the trade talks, but insisted he will intervene to force them through.
"There are going to be sensitivities on both sides, there are going to be politics on both sides, but if we can look behind the narrow concerns to stay focused on the big picture, the economic and strategic importance of this partnership, I am hopeful we can achieve the kind of high-standard, comprehensive agreement that the global trading system is looking to us to develop," he said.
"We are going to give a strong mandate to our negotiators, but occasionally I suspect we are going to have to intervene and break through some logjams. Nevertheless, I am confident we can get it done."
European Council president Herman van Rompuy reflected a sense that the trans-Atlantic pact represents the best chance for the old powers of Europe and America to compete with emerging giants like China and India when he said: "The Atlantic is not the past. It is also the future."
Mr Obama arrived on board Air Force One at Belfast's Aldergrove International Airport this morning for his first visit to Northern Ireland, accompanied by wife Michelle and daughters Malia, 14, and Sasha, 11.
In an impassioned speech at the city's Waterfront conference centre, the President said that 15 years after the Good Friday Agreement, Northern Ireland was setting an example for people all over the world seeking to escape apparently intractable religious, national and ethnic conflicts.
"They are wondering 'Perhaps, if Northern Ireland can achieve this, we can too'," said Mr Obama. "You are their blueprint to follow, you are their proof of what is possible. Because hope is contagious."
But it was the conflict in Syria which dominated Mr Obama's talks shortly afterwards with Mr Cameron as the two leader travelled in the President's armoured limousine, nicknamed The Beast.
And the two-year civil war will be the main topic of discussions between leaders of the G8 countries - the UK, US, France, Germany, Italy, Canada, Japan and Russia - at the official summit dinner in the luxury Lough Erne golfing resort this evening.
London mayor Boris Johnson warned today against arming the anti-Assad rebels, saying that British weapons could end up in the hands of "al Qaida-affiliated thugs". But Foreign Secretary William Hague said Britain must protect the Syrian opposition from being "exterminated", warning that the crisis was "on a trajectory to get worse".
In a round of TV interviews, Mr Cameron said: "Let's be clear - I am as worried as anybody else about elements of the Syrian opposition, who are extremists, who support terrorism and who are a great danger to our world.
"The question is what do we do about it? My argument is that we shouldn't accept that the only alternative to Assad is terrorism and violence.
"We should be on the side of Syrians who want a democratic and peaceful future for their country and one without the man who is currently using chemical weapons against them.
"What we can try and do here at the G8 is have further pressure for the peace conference and the transition that is needed to bring this conflict to an end."
Lough Erne is the first G8 summit to be hosted in the UK since Gleneagles in 2005, and was taking place behind tight security, with 8,000 police mounting a ring of steel around the venue.
Mr Cameron has used his year-long presidency of the body to seek international agreements on his economic priorities of trade, tax and transparency.
He is tomorrow hoping to forge agreement on greater sharing of tax information to prevent companies and individuals avoiding paying their fair share by hiding cash in offshore bolt-holes.
"I want to be absolutely clear that my agenda here is about helping hard-working families right here in the United Kingdom," he said.
"If we sign trade deals and start trade negotiations here at this meeting in Northern Ireland, that will cut prices and mean a wider range of goods in shops here in the United Kingdom and jobs here in the United Kingdom.
"So my focus is very clear - getting agreements, signing deals, making progress on issues that will help hard-working families right here in the United Kingdom. For me, that's what the agenda of this G8 is all about."