U.S. President Barack Obama faces what could be a frosty G8 meeting with Vladimir Putin on Monday after the Russian leader clashed with the West over plans to arm Syrian rebels fighting President Bashar al-Assad.

At their first face-to-face meeting in a year, Obama will try to convince Putin to bring Assad to the negotiating table but the Kremlin chief has warned the West it risks sowing turmoil across the Middle East by stoking the conflict.

British Prime Minister Cameron, who chairs the G8 summit, acknowledged there was "a big difference" between the positions of Russia and the West on Syria, but stressed there was also common ground between the world's richest powers.

But as G8 leaders gathered at a resort in Northern Ireland, Russia said it would not permit no-fly zones to be imposed over Syria.

"I think we fundamentally would not allow this scenario," Foreign Ministry spokesman Alexander Lukashevich said in Moscow.

On Sunday, Putin had described Assad's foes as cannibals who ate their enemies' intestines in front of media cameras.

"Are these the people you want to support? Is it them who you want to supply with weapons?" Putin said in London on his way to the G8.

Canadian Prime Minister Stephen Harper was equally blunt, saying that Putin, Assad's only big-power ally at the G8 table, was supporting thugs.

"We are not, unless there is a big shift in position on his part, going to get a common position with him at the G8."

The United States said last week it would step up military aid to Syrian rebels - a move which officials said would involve supplying the Western-backed Supreme Military Council with automatic weapons, light mortars and rocket-propelled grenades.

The European Union has also dropped its arms embargo on Syria, allowing France and Britain to arm the rebels, though the two countries say they have no immediate plans to do so.

Obama and Putin are due to meet at about 6:30 pm local time

(0530 GMT) at the Lough Erne golf resort about 10 km (7 miles) outside the Northern Irish town of Enniskillen, scene of an IRA bomb attack in 1987 that killed 11 people.

Security was tight and the venue was surrounded by a 6-foot-high steel fence, though Cameron was keen to showcase the relative peace in Northern Ireland as it tries to attract investment after decades of trouble.

In a speech in Belfast, Obama urged young people in Northern Ireland to finish making "permanent peace" and set an example to other areas of the world stricken by conflict.

Cameron could also face some awkward questions at the G8 table after a Guardian newspaper report that Britain spied on officials taking part in two Group of 20 meetings in 2009.

U.S.-EU TRADE TALKS

The leaders of the United States, Japan, Canada, Russia, Germany, France, Britain and Italy - representing just over half of the $71.7 trillion global economy - will also discuss global economy and trade.

The leaders of the EU and United States are due to announce the start of formal negotiations on a free trade deal that could be worth more than $100 billion a year to each economy.

"What you are going to see today is good and important news on the launch of the EU-U.S. trade negotiations," a spokesman for Cameron said.

Japanese Prime Minister Shinzo Abe, German Chancellor Angela Merkel and other leaders will probably discuss the role of central banks and monetary policy.

They are likely to say they are not content with progress so far in fixing their economies in the wake of the global financial crisis, according to a draft communique seen by Reuters.

Japan's Abe will use the opportunity to explain his cocktail of fiscal and monetary stimulus known as 'Abenomics' to the leaders as investors try to absorb the implications of a signal by the U.S. Federal Reserve it may start to slow its money-printing.

Fed chairman Ben Bernanke will not attend. He and his colleagues hold a policy meeting on Tuesday and Wednesday.

TREASURE ISLAND TAX

Cameron has made tackling tax avoidance - which campaigners say costs about $3 trillion a year - a main part of the formal agenda at the summit.

He has turned up the pressure to clamp down on secretive money flows by pressing Britain's overseas tax havens into a transparency deal and announcing new disclosure rules for British firms.

Representatives of overseas tax havens linked to Britain on Saturday agreed to sign up to an international transparency protocol. Aid campaigners said Britain's action will count for little if the rest of the G8 does not follow suit.

G8 leaders will probably shy away from adopting a measure aimed at curbing tax avoidance by highlighting when companies channel profits into tax havens, and will include a watered-down alternative, according to the draft communique.

"I particularly care that we track down tax evaders, especially to end tax avoidance," Merkel told German TV Station RTL. "That only works through international cooperation."