As Israel tightened its grip on a strategic border village seized in south Lebanon, Syria fuelled fears the fighting could spread by issuing a warning that it would intervene if Israel dared launch a full-out invasion of Lebanon.
US Secretary of State Condoleezza Rice was also heading to the Middle East with Washington increasingly estranged from European and Arab allies over a conflict that has killed close to 400 people in just 12 days and triggered a major humanitarian crisis.
UN humanitarian co-ordinator Jan Egeland, in Beirut to launch a urgent appeal for funds for half a million people made homeless by the conflict, made no attempt to hide his fury as he toured bombed-out areas.
"This is destruction of block after block of mainly residential areas. I would say it seems to be an excessive use of force in an area with so many citizens," he told reporters in the southern suburbs of Beirut, a Hezbollah stronghold.
Asked if the Israeli raid that destroyed the burned-out buildings before him constituted a war crime, he replied: "It makes it a violation of humanitarian law."
His comments came as at least twelve civilians, including a Lebanese press photographer, were killed in new Israeli air strikes across Lebanon on the 12th day of Israel's punishing war on Hezbollah.
Hizbollah said three of its fighters had also been killed.
Its guerrillas responded with a new hail of rocket fire on Israel's third city of Haifa, killing one person in his car and a second as he worked in a warehouse.
Streams of people, many waving white flags, are making a desperate trek from southern Lebanon after Israel ordered them to leave their homes, raising fears it was planning a large scale ground invasion.
Israeli Justice Minister Haim Ramon said the aim of the offensive was to keep Hezbollah - which controls southern Lebanon in the absence of the regular Lebanese army - at least 20 kilometres from the frontier.
Israel, which has called up thousands of reserve soldiers and massed its troops on the border, seized control of the strategic hilltop village of Marun Al-Ras on Saturday after sending tanks, bulldozers and armoured cars rolling across the border.
But Defence Minister Amir Peretz insisted Israel did not plan a wide-scale invasion. "The ground operation is focusing on a limited entry of forces," he told the cabinet. "We are not dealing with an invasion of Lebanon."
At least 362 people have been killed in Israel's massive blitz against Lebanon which was launched after the capture of two soldiers by Hezbollah guerrillas in a deadly border attack on July 12. A total of 37 Israelis have died.
Israel's ambassador to the United States maintained the military offensive had dealt a "real blow" to Hezbollah, damaging the group's arsenal and killing a "few hundred" of its fighters.
Daniel Ayalon said the military campaign was "not easy" but Israel was making progress, adding: "And in a few days, you will see a totally different situation."
But in the first openly expressed reservations by an Israeli minister on the success of the offensive, minister without portfolio Eitan Cabel said: "I admit I had hoped for better from the army."
Syria, blamed by the United States for stoking the conflict, warned that if Israel invaded Lebanon it would have no choice but to respond.
"If Israel makes a land entry into Lebanon, they can get to within 20 kilometres of Damascus," Information Minister Moshen Bilal told the Spanish newspaper ABC.
"What will we do? Stand by with our arms folded? Absolutely not. Without any doubt Syria will intervene in the conflict."
US ambassador to the United Nations John Bolton rebuffed a previous Syrian offer of dialogue in characteristically blunt fashion, saying that "Syria doesn't need dialogue to know what they need to do."
Israeli Prime Minister Ehud Olmert, whose army is also fighting a second deadly offensive in the Gaza Strip, said he would accept a peacekeeping force in Lebanon "made up of troops from European Union countries".
Its mandate "will have to include control of the border crossings between Syria and Lebanon, deployment in south Lebanon and support for the Lebanese army," he said.
His comments came amid mounting international criticism of the Israeli offensive, which has left Lebanon virtually cut off from the world, made hundreds of thousands refugees in their own country and destroyed billions of dollars of infrastructure.
Even a minister from close US ally Britain, which had drawn Arab anger for appearing to back US support of the bombardment, has described Israel's tactics as "very difficult to understand".
Rice was due to arrive in Israel on Monday to meet Olmert in the hope of finding a long-term solution to the crisis rather than a temporary cease-fire, an outcome vehemently opposed by Washington as a "false promise".
Israel said it opened an 80-kilometre by eight-kilometre (50-mile by five-mile) safe passage to Beirut for ships and aircraft, a humanitarian corridor to allow aid to the Lebanese. Israel's air and sea blockade put Lebanon's only international airport out of action, and the bombing of houses, roads, bridges, factories, warehouses and trucks has created scenes reminiscent of the 1975-1990 civil war.
Foreign governments have been forced to lay on a flotilla of ferries, warships and cruise liners to evacuate stranded nationals, mainly to the nearby resort island of Cyprus which has been battling to find temporary accommodation and flights for the estimated 70,000 evacuees at peak summer holiday season.