David Cameron is today hoping to kick off the G8 summit in Northern Ireland with progress on a free trade deal between Europe and the US which he believes could "turbo-charge the transatlantic economy".
US President Barack Obama and European leaders are expected to launch formal negotiations on the pact - dubbed an "economic Nato" - which the Prime Minister believes could be worth £10 billion to the UK economy, or £380 for every British household.
But the summit in Lough Erne is set to be overshadowed by international tensions over Syria, after Russian President Vladimir Putin made clear his continued opposition to Western countries arming rebels trying to oust Bashar Assad.
In a blunt warning after talks with Mr Cameron at 10 Downing Street, Mr Putin said the West should not arm insurgents who "eat the organs" of their enemies.
The brutal behaviour of some rebel groups was inconsistent with the "humanitarian and cultural values" of Europe, warned the Russian President, who defended his own supply of arms to the Assad regime.
Mr Obama - who will meet Mr Cameron ahead of the formal opening of the summit - has indicated he is ready to send weapons to opposition fighters, after Assad crossed his "red line" by using chemical weapons on his own people.
While acknowledging deep differences between Moscow and the West, the PM said the challenge at Lough Erne was to "focus on the common ground where we both want to see a peace process, a transition, take place".
Mr Putin agreed that the G8 gathering - which brings together leaders of the UK, US, Russia, France, Germany, Italy, Canada and Japan - was one of the most appropriate forums for discussing a conflict "which can be resolved only by political and diplomatic means".
The situation in Syria will be discussed over a working dinner this evening.
But the first topic on the agenda as the summit opens amid high security will be the world economy.
As president of the G8 for the first time since Tony Blair hosted the Gleneagles summit in Scotland in 2005, the UK is seeking agreements on trade, tax evasion and financial transparency which Mr Cameron believes could "drive growth and prosperity all over the world".
Top of the agenda is the EU/US trade pact, which cleared its latest obstacle in last-minute talks on Friday, when Europeans agreed a "mandate" for their negotiators after delays caused by French insistence on protecting its film, TV and music industries from US imports.
The Prime Minister and Mr Obama will now meet EU members of the G8 - Chancellor Angela Merkel of Germany, French President Francois Hollande, Italy's Prime Minister Enrico Letta and the presidents of the European Commission and Council, Jose Manuel Barroso and Herman van Rompuy - with the aim of waving the starting flag for formal negotiations to begin.
Spelling out what he sees as the potentially "transformative" value of the deal, Mr Cameron said: "An EU-US trade deal... could be worth £10 billion to the UK alone - in the end that's not some abstract statistic, these trade deals matter, because they mean more jobs, more choice for consumers and lower prices."
Tomorrow, attention will shift to counter-terrorism - including Mr Cameron's proposals for a block on states paying ransoms for their kidnapped citizens - and action against tax havens.
The Prime Minister's tax transparency agenda was boosted at the weekend when 10 British overseas territories and crown dependencies agreed to sign up to an OECD initiative to share information with international tax authorities about companies' and individual's offshore accounts.
Mr Cameron said the agreement would add momentum to the drive to get the G8 to crack down on tax evasion and aggressive tax avoidance by showing that Britain was "getting our own house in order".
Campaigners from development charities are trying to stoke up pressure on the world leaders to shine a light on the tax havens, which they believe are denying poor countries vital revenues running into billions of pounds.
Setting out his agenda for the two days of talks, Mr Cameron said he was "determined to use this opportunity to address some of the biggest issues facing our countries" and agree "practical action which will make a difference for our own peoples and for the wider world".
He said: "I want a meeting where we can look each other in the eye, cut through the obstacles and the opposition and generate the political will to solve the problems we face."
Hosting the summit in Northern Ireland, 15 years after the Good Friday Agreement, would "help inspire progress and dispel cynicism" by showing how even the most intractable problems can be addressed and resolved through political leadership and constructive dialogue, he said.
Economic recovery remains "the most important issue" facing G8 countries, with a need to create jobs and reduce poverty around the world, said Mr Cameron.
He made no apology for not putting aid at the centre of his agenda, as Mr Blair did at Gleneagles.
"We are leading a new approach that gets right to the causes of poverty, not the symptoms of the poverty," said Mr Cameron. "But I want to ensure that this a summit that brings together the developed and developing world and tackles issues relevant to us all."