Leaders of the G8 industrial nations are meeting on Saturday under growing pressure to stem spiralling Mideast violence but are sharply divided over Israeli military strikes on Lebanon which entered a fourth day.
US President George Bush, who was holding a second round of bilateral talks with Russian leader Vladimir Putin before the meeting, insisted that Israel must have the right to defend itself.
Officials said the US had no plans to pressure Israel to halt its military operations aimed at Hezbollah militants who are holding two captured Israeli soldiers.
"The president is not going to make military decisions for Israel," said Bush's spokesman Tony Snow.
Putin, who is hosting Russia's first ever G8 summit, announced he was adding the Middle East crisis to the three-day meeting's already packed agenda.
"We will press all the parties to immediately end the bloodshed," said Putin.
But Moscow is taking a much different stance to Washington regarding Israeli military actions.
Russian Foreign Minister Sergei Lavrov condemned the Israeli attacks as "a disproportionate response". He said: "I think that all this will develop in a very dramatic and tragic way."
As a club of the world's richest and most powerful countries, this year's G8 summit will likely be measured on whether leaders can show unity on the Mideast crisis and broker some kind of ceasefire.
The G8 members are Britain, Canada, France, Germany, Italy, Japan, Russia and the US. G8 leaders are expected to address the Israeli-Lebanese violence at an informal working dinner on Saturday evening.
So far, the only G8 leader who appears to be backing Bush on Israel appears to be Canadian Prime Minister Stephen Harper. French President Jacques Chirac criticised Israel for its excessive reaction. "I ask myself if this is not an attempt to destroy Lebanon," said Chirac.
All four EU G8 members - France, Germany, Britain and Italy - have backed calls for Israeli restraint.
The Israeli-Lebanon conflict is not the only crisis topping the summit agenda. Leaders are also due to discuss Iran's uranium enrichment programme, which is widely believed to be aimed at building nuclear weapons.
North Korea's missile tests last week are expected to be raised by Japan and the US, which are seeking tougher sanctions against the Pyongyang government.
President Putin has formally made energy security the top summit issue. But even here, there are expected to be differences among G8 leaders given controversy over Russia's brief cut-off of natural gas to Ukraine last January over a pricing dispute.
Leaders will also seek a way forward on stalled World Trade Organisation (WTO) talks.