US President Barack Obama and world leaders arrived in Northern Ireland for the G8 summit on Monday looking to put pressure on Russia to back away from its support of Syrian President Bashar al-Assad.
Hours before the summit was due to begin, host Prime Minister David Cameron said his priority for the meeting was to ensure a peace conference on the Syria conflict takes place later this year.
But amid rising tensions over Syria, talks between Obama and Russian President Vladimir Putin were set to be prickly, with both leaders now offering military support to opposing sides in the war.
"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," Cameron said in a round of television interviews before the summit began.
"We (Britain) haven't made a decision to give any arms to the Syrian opposition but what we do need to do is bring about this peace conference and this transition, so that people in Syria can have a government that represents them, rather than a government that's trying to butcher them," he said.
Obama's Air Force One jet landed in a rainy Belfast shortly after 8:35 am (0735 GMT) and he headed to a local conference centre to speak to an audience of 2,000 mostly young people, touching on Northern Ireland's peace process.
"You are the first generation in this land to inherit more than just hardened attitudes, and the bitter prejudices of the past. You are an inheritor of a just and harder peace," Obama said.
After meeting Cameron in London on Sunday, Putin insisted that Moscow had abided by international law when supplying weapons to Assad's regime and demanded that Western countries considering 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.
Obama will emphasise to Putin that Washington wants to keep alive the mooted peace conference in Geneva co-organised with Moscow, which appears to be slipping down the list of priorities.
Cameron also hopes the G8 summit, held in the 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 8,000 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 2,000 protesters to take part in an anti-G8 march in Enniskillen on Monday.
Figures were revised downwards after just 1,500 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.