The Bush administration, backed by Britain, has blocked efforts for an immediate halt to the fighting initiated at the UN security council, the G8 summit in St Petersburg and the European foreign ministers' meeting in Brussels.

"It's clear the Americans have given the Israelis the green light. They [the Israeli attacks] will be allowed to go on longer, perhaps for another week," a senior European official said yesterday. Diplomatic sources said there was a clear time limit, partly dictated by fears that a prolonged conflict could spin out of control.

US strategy in allowing Israel this freedom for a limited period has several objectives, one of which is delivering a slap to Iran and Syria, who Washington claims are directing Hizbullah and Hamas militants from behind the scenes.

George Bush last night said that he suspected Syria was trying to reassert its influence in Lebanon. Speaking in Washington, he said: "It's in our interest for Syria to stay out of Lebanon and for this government in Lebanon to succeed and survive. The root cause of the problem is Hizbullah and that problem needs to be addressed."

Tony Blair yesterday swung behind the US position that Israel need not end the bombing until Hizbullah hands over captured prisoners and ends its rocket attacks. During a Commons statement, he resisted backbench demands that he call for a ceasefire.

Echoing the US position, he told MPs: "Of course we all want violence to stop and stop immediately, but we recognise the only realistic way to achieve such a ceasefire is to address the underlying reasons why this violence has broken out."

He also indicated it might take many months to agree the terms of a UN stabilisation force on the Lebanese border.

After Mr Blair spoke, British officials privately acknowledged the US had given Israel a green light to continue bombing Lebanon until it believes Hizbullah's infrastructure has been destroyed.

Washington's hands-off approach was underlined yesterday when it was confirmed that Condoleezza Rice, the US secretary of state, is delaying a visit to the region until she has met a special UN team. She is expected in the region on Friday, according to Dan Gillerman, Israel's ambassador to the UN.

The US is publicly denying any role in setting a timeframe for Israeli strikes. When asked whether the US was holding back diplomatically, Tony Snow, the White House's press spokesman, said yesterday: "No, no; the insinuation there is that there is active military planning, collaboration or collusion, between the United States and Israel - and there isn't ... the US has been in the lead of the diplomatic efforts, issuing repeated calls for restrain,t but at the same time putting together an international consensus. You've got to remember who was responsible for this: Hizbullah ... It would be misleading to say the United States hasn't been engaged. We've been deeply engaged."

Steven Cook, a specialist in US-Middle East policy at the Washington-based Council on Foreign Relations, said: "It's abundantly clear [that US policy is] to give the Israelis the opportunity to strike a blow at Hizbullah ...

"They have global reach, and prior to 9/11 they killed more Americans than any other group. But the Israelis are overplaying their hand."

Israel is already laying the ground for negotiations. "We are beginning a diplomatic process alongside the military operation that will continue," said Tzipi Livni, Israel's foreign minister, yesterday. "The diplomatic process is not meant to shorten the window of time of the army's operation, but rather is meant to be an extension of it and to prevent a need for future military operations," she added.

Moshe Kaplinsky, Israel's deputy army chief, said the offensive could end within a few weeks, adding that Israel needed time to complete "clear goals". Israeli officials said fighting could begin to wind down after the weekend, if Hizbullah stops firing rockets.

A peace formula is also beginning to emerge: it includes an understanding on a future prisoner exchange, a deployment of the Lebanese army up to the Israeli border, a Hizbullah pullback, and the beefing up of an international monitoring force. For the first time, Ms Livni suggested Israel might accept such a force on a temporary basis.

There were signs of differences of emphasis between the Foreign Office and Downing Street over the conflict.

Kim Howells, a Foreign Office minister, explicitly called for the US to rein in Israel. "I very much hope the Americans will be putting pressure on the Israelis to stop as quickly as possible." he told the BBC. "We understand the pressure the Israeli government is under, but we call on them to look very carefully at the pressure ordinary people are under in southern Lebanon and other parts of Lebanon too ... We want to stop this as quickly as possible".

Israeli airstrikes killed 31 yesterday, including a family of nine in Aitaroun. More than 230 civilians in Lebanon have been killed in the past week.

An Israeli man was killed by a Hizbullah rocket in Nahariya in northern Israel, bringing the total of Israeli civilian deaths to 13. The army said 50 missiles were fired yesterday at northern Israel, injuring at least 14 people.

Flashpoints

· 31 Lebanese killed in Israeli air raids. Nine members of one family were killed and four wounded in a strike on their house in the village of Aitaroun. Five were killed in other strikes in the south and two in the Bekaa Valley. An attack on a Lebanese army barracks east of Beirut killed 11 soldiers and wounded 30. A truck carrying medical supplies was hit and its driver killed on the Beirut-Damascus highway. Hizbullah says one of its fighters was killed.

· One man killed as he was walking to a bomb shelter in Nahariya, northern Israel. The army said Hizbullah fired 50 missiles, hitting the port and railway depot at Haifa, as well as the towns of Safed, Acre and Kiryat Shmona.

· Hundreds evacuated from Beirut in helicopters and boats. HMS Gloucester arrives to start evacuation of Britons. The Orient Queen, a cruise ship capable of carrying 750, sets out from Cyprus, escorted by a US destroyer.