The Israeli air force strikes severed Lebanon's last significant road link to Syria, stopped a convoy carrying 150 tonnes of relief and cut what the UN called its "umbilical cord" for aid supplies.

Five Lebanese civilians were killed and 19 wounded in the bombing raids, which hit Christian areas in which Hizbollah has little support or presence.

More than two dozen farm workers died in a separate air strike near the Lebanon-Syria border.

The Israeli army said three of its soldiers were killed by an anti-tank missile during fighting in southern Lebanon, and an army spokesman said at least seven Hizbollah fighters had been killed during fighting in the Lebanese town of Markaba.

Israel said it had destroyed the bridges along Lebanon's main north-south coastal road to prevent Syria from rearming Hizbollah, which is also backed by Iran.

However, the European commission said the bombing had made it harder to deliver humanitarian relief.

"We will need guarantees for the safety of our people on the ground if we are to successfully continue the provision of aid," Louis Michel, the European commissioner for humanitarian aid, said.

"The bombing of roads that have been previously cleared as safe for evacuation and humanitarian aid could have a major impact on the delivery of our aid."

Christiane Berthiaume, of the UN World Food Programme, said: "This [road] is Lebanon's umbilical cord. This has been the only way for us to bring in aid."

The bridge at Maameltein, just north of Beirut, was split down its centre. Further north, the ruins of another bridge lay in the valley it once spanned.

"The whole road is gone," Astrid van Genderen Stort, a senior information officer for the UNHCR refugee agency, said. "It's really a major setback, because we used this highway to move staff and supplies into the country."

The World Food Programme said a convoy carrying supplies and emergency personnel to Beirut today was stuck. Although UN trucks may be able to take secondary roads, this would slow down aid shipments.

UN teams have so far been refused permission to assess the damage caused by the bombing, Ms Berthiaume said.

Security officials and witnesses said a Lebanese soldier and four civilians were killed in separate Israeli air raids near Beirut's airport and southern suburbs.

The UN called off planned convoys to the southern port city of Tyre after air raids on a Beirut suburb prevented drivers from reaching the assembly point.

The broadened bombing campaign came as Hizbullah guerrillas unleashed another day of rocket attacks on Israel. Hizbullah fighters fired 45 rockets in less than a half hour, killing four Israelis, three of them Arabs.

Farm workers killed

Four Israeli missiles hit a refrigerated warehouse where farm workers were loading vegetables near the Lebanon-Syria border, killing at least 33 people and wounding 20, local officials said.

The attack happened at a farm near the town of al-Qaa, a Hizbullah stronghold around six miles from Hermel that has been hit by Israeli air strikes at least three times.

An Israeli army spokesman said air strikes in the area had targeted two buildings that military intelligence had shown were being used by Hizbollah to store weapons.

However, television footage showed the bodies of what appeared to be farm workers near the ruins of a small structure in fruit groves. Fruit baskets were strewn nearby.

It was the second deadliest strike in Lebanon after the air raid that killed up to 54 civilians in the village of Qana on Sunday.

At least 720 people in Lebanon and 74 Israelis have been killed in the conflict so far.

Israel has put more than 10,000 troops into Lebanon, and says it has carved out a zone containing 20 villages up to 7km from its border. The army has been ordered to prepare for a possible push further north.

The US and France today continued negotiations on a UN resolution aimed at securing a ceasefire backed by an international force more robust than the UN peacekeepers already in south Lebanon.

Once they reach agreement - which officials said could happen over the weekend - a UN security council vote could take place within 24 hours.

The US ambassador to the UN, John Bolton - speaking after several hours of talks with the French UN ambassador, Jean-Marc de la Sabliere - said progress had been made and a text was being sent back to Washington and Paris for review.

Washington wants an international force in southern Lebanon immediately after a truce, while France - a likely leader of the force - wants the troops to move in only after a permanent ceasefire.