Tony Blair has flown to Russia for the G8 summit, amid calls for action to tackle problems in the Middle East and Africa.
Tony Blair will give an update on the work done in Africa
Talks between the leaders of eight of the world's most powerful nations are expected to focus on energy and trade.
But Oxfam is urging them to try to find solutions to the "humanitarian crises" in Darfur and Israel, Lebanon and the Palestinian Territories.
The three-day summit will officially open in St Petersburg on Sunday.
On Saturday night Mr Blair, accompanied by his wife Cherie, will join fellow G8 leaders from Russia, the US, Canada, France, Germany, Italy and Japan at an informal welcoming dinner.
Middle East situation
The prime minister will have a breakfast meeting with President George W Bush on Sunday morning, during which they are expected to discuss the mounting tension in the Middle East.
Mr Blair's official spokesman said there was now a "very serious situation" in the region, adding: "The implications are very serious and we need to address it with urgency."
He said Britain wanted to "try and see what is the process that would underpin how we de-escalate the situation".
"This shouldn't just be a talking shop it should be setting an agenda which will help de-escalate the situation."
And he insisted: "Inevitably in this situation, people will play the blame game. We are not going to get into that."
Mr Blair will also discuss the Middle East with United Nations Secretary General Kofi Annan on Monday, the last day of the three-day summit.
Oxfam's Jo Leadbeater warned that violence was getting worse in Darfur, despite G8 pledges to support peacekeeping efforts.
And she called on the leaders to urge restraint in the Middle East.
"This meeting is happening against a backdrop of rapidly deteriorating humanitarian crises which the G8 leaders must not turn their back on," she said.
The Blairs will join other leaders for an informal dinner
The prime minister acknowledged that the Middle East and Africa would command attention alongside Iran, energy and climate change.
But he said he would not try to bring countries into line with the Kyoto Protocol.
Mr Blair is due to make a presentation to fellow leaders on Monday on the progress made on Africa since last year's summit, which was held at Gleneagles in Perthshire.
Liberal Democrat international development spokeswoman Susan Kramer said the summit was a chance to break the deadlock in the World Trade Organisation talks on fairer trade for poor countries.
"Much has been made of Tony Blair's close relationship with President Bush. This is the time to turn it to account," she said.
"If the G8 fails to act, it is the developing world that will pay the price."
The G8 countries will be joined by delegates from nations including India, China, South Africa, Mexico and Brazil.
Anti-globalisation protests are also expected, with more than 1,000 demonstrators reported to be preparing to make their voices heard at the three-day summit, though they will be kept miles away from the leaders.