VATICAN CITY (AFP) - Pope Francis on Sunday called on the leaders of the world's top industrialised nations meeting in Northern Ireland to push for an immediate ceasefire in Syria.

On the eve of the two-day G8 summit, the Pope wrote to British Prime Minister David Cameron, calling on the powers to act fast to end a conflict that has claimed tens of thousands of lives.

"I earnestly hope that the summit will help to obtain an immediate and lasting ceasefire and to bring all parties in the conflict to the negotiating table," he said.

"Peace demands a far-sighted renunciation of certain claims, in order to build together a more equitable and just peace," he said, without elaborating.

The West is at odds with Russia over what action to take to end an escalating civil war that has killed at least 93,000 people since March 2011, according to United Nations figures.

Washington has vowed to send military aid to rebel forces battling to topple President Bashar al-Assad after saying it had proof that the regime had crossed a "red line" by using chemical weapons on a small scale - but Russia is dismissive of the claims by the United States.

Pope Francis also called for the G8 leaders to ensure that any measures adopted at the summit to tackle the financial crisis have a strong ethical line.

While Syria is set to dominate the agenda, Mr Cameron has been promising developments on clamping down on tax evasion and easing bank secrecy.

"Urgent measures to resolve the global economic crisis must be guided by the ethics of truth," Pope Francis said.

"This includes, first and foremost, respect for the truth of man, who is not simply an additional economic factor, or a disposable good, but is equipped with a nature and a dignity that cannot be reduced to simple economic calculus," he added.

The 76-year-old Argentine - who has made giving a voice to the poor one of the keystones of his papacy - called on the leaders to remember those less fortunate in their economic calculations.

"The goal of economics and politics is to serve humanity, beginning with the poorest and most vulnerable wherever they may be, even in their mothers' wombs," he said.

"Every economic and political theory or action must set about providing each inhabitant of the planet with the minimum wherewithal to live in dignity and freedom."