Syria tops the agenda at the two-day G8 summit, with leaders hoping to pressure Russia to support an initiative that will end the conflict.
World leaders are heading to the G8 summit in Northern Ireland looking to put pressure on Russia to back away from its support of Syrian President Bashar al-Assad amid growing Western efforts to arm the rebels.
British Prime Minister David Cameron, the host of the meeting of top industrialised powers, insisted he could overcome his differences with Russian President Vladimir Putin after they held pre-summit talks in London.
Amid rising tensions over Syria, Putin will meet US President Barack Obama in Northern Ireland on Monday for what could be prickly talks, as both leaders now offer military support to opposing sides in the war.
In London, Putin insisted that Moscow had abided by international law when supplying weapons to Assad's regime and demanded that Western countries contemplating arming rebels do the same.
"We are not breaching any rules and norms and we call on all our partners to act in the same fashion," Putin said.
The Russian leader referred to a video released last month purportedly showing a rebel Syrian fighter eating the heart of a dead soldier.
He asked if the West really wanted to support rebels "who not only kill their enemies, but open up their bodies and eat their internal organs in front of the public and the cameras".
But Cameron said: "What I take from our conversation today is that we can overcome these differences if we recognise that we share some fundamental aims: to end the conflict, to stop Syria breaking apart, to let the Syrian people decide who governs them and to take the fight to the extremists and defeat them."
Obama will emphasise to Putin that Washington wants to keep alive a mooted Geneva peace summit co-organised with Moscow, which appears to be slipping down the list of priorities.
Cameron also hopes the two-day G8 summit, held in the luxury lake-fringed Lough Erne golf resort, will see the formal start of negotiations on a vast free trade pact between the European Union and the United States.
EU nations agreed to go ahead with the talks after late-night discussions in Luxembourg on Friday to convince France that its prized cultural industries would not be under threat from the pact.
The British hosts of the gathering also want to forge consensus on cracking down on tax evasion and making multinational companies more transparent.
Counter-terror measures will also feature with Britain pushing for a commitment that ransoms will not be paid in the event of kidnapping by militants - something it feels is not being adhered to by all G8 nations.
Britain is keen to push the issue following a hostage crisis at a gas plant in Algeria in January in which 37 foreign hostages were killed, among them six Britons.
The summit is surrounded by the biggest security operation in Northern Ireland's troubled history, with around 8000 officers on duty.
Heavily armed police in armoured Land Rovers are stationed at frequent intervals along the country roads leading to the summit venue near the town of Enniskillen.
Police say the expected anti-globalisation demonstrations have been smaller than expected so far.
They expect around 2000 protesters to take part in an anti-G8 march in Enniskillen on Monday.
Figures were revised downwards after just 1500 anti-capitalists turned up for a rally which passed off without incident in Belfast on Saturday - 10,000 demonstrators had been expected to attend the two protests there.
Police fear that dissident republican extremists opposed to the peace process in Northern Ireland might seek to launch an attack in Belfast.
Cameron will host Obama, Putin, German Chancellor Angela Merkel, French President Francois Hollande, Japanese Prime Minister Shinzo Abe, Italian Prime Minister Enrico Letta and Canadian Prime Minister Stephen Harper at the summit.
Other leaders invited are from the EU, Mexico, Libya and Ethiopia.