At least 30 were injured in the strike, which capped another day of violence in Lebanon in which more than 50 people died, including three Israeli soldiers.

As night fell, Israel declared a curfew in southern Lebanon, warning that all vehicles apart from humanitarian traffic would be at risk. Ground forces continued to run into fierce resistance in southern Lebanon. Hizbullah militants fired more than 100 rockets into northern Israel, wounding at least one.

But the Beirut attack was the day's bloodiest episode. Last night, local residents and rescue workers scrambled through the rubble and debris in the dark as the insides of an eight-storey building spilled out into a narrow street. Water from a burst pipe in a building opposite sprayed out a fine mist across the wreckage. Neighbouring residents, now stuck in teetering buildings, peered out of the back half of their sitting rooms as splintered furniture dangled out on the street below. A women in her nightdress on the sixth floor tried to retrieve something on what was left of her balcony as a chunk of her front room crashed down on to the street. An ambulance worker said he had counted 10 bodies so far. At least two were children.

Lebanese officials said there were many reports of other casualties throughout southern Lebanon but rescue workers were not able to reach the sites because of continued Israeli airstrikes. Israel also threatened to attack UN peacekeepers if they attempted to repair bomb-damaged bridges in southern Lebanon. UN officials contacted the Israeli army to inform them that a team of Chinese military engineers attached to the UN force in Lebanon intended to repair the bridge on the Beirut to Tyre road to enable the transport of humanitarian supplies.

According to the UN, Israeli officials said the engineers would become a target if they attempted to repair the bridge.

Senior UN officials reacted angrily to the destruction of a temporary causeway over the Litani river overnight. "We must be able to have movement throughout the country to deliver supplies. At this point we can't do that," said David Shearer, the humanitarian coordinator for Lebanon. "The deliberate targeting of civilian infrastructure is a violation of international law."

International aid groups have blamed Israel for not providing security guarantees, thereby paralysing the delivery of aid to the south. Even when aid reaches Tyre, convoys have to apply on a case by case basis for permission to take it out to the villages. Most applications are refused.

A convoy run from Beirut to Tyre by Médecins sans Frontières yesterday was forced to stop at the ruins of the causeway. Boxes of medicine were carried over a footbridge by hand and loaded up into separate vehicles on the other side.

Car passengers had to do the same, driving to the footbridge and waiting for transport on the other side.

Israel's army warned residents in southern Lebanon to remain indoors after 10pm yesterday and said anyone moving after that would be at risk. "Anyone who does travel is taking a high risk. There is no end period," an Israeli military source said. "This will allow us to track anyone potentially trying to launch rockets."

The source said the restriction on movement applied anywhere south of the Litani river, which is roughly 13 miles from Israel's northern border. He did not specify how the warning had been delivered.

Israel also said it shot down a Hizbullah drone."We located it over Lebanon and tracked it over the Mediterranean where we shot it down. Naval vessels picked up the debris for investigation," an Israeli military spokesman said. The Israeli army said it could not immediately say if it was carrying explosives.

Tyre was rocked yesterday by fresh Israeli airstrikes. Four buildings on the northern outskirts were crushed in pinpoint strikes which left adjacent buildings standing. The four destroyed buildings included the flat where the Israeli commandos had killed the two alleged Hizbullah leaders on Saturday.