One soldier died and two were injured in the Bekaa Valley operation.

Lebanese sources earlier told Reuters agency that three militants also died.

The incident came hours after UN chief Kofi Annan warned of a "fragile" situation on the ground.

Meanwhile, 50 French troops arrived in the Lebanese port of Naqoura, the first soldiers to bolster the UN force.

They are among 200 extra troops promised by France, as the UN struggles to build its force.

The UN wants 3,500 troops on the ground speedily, to be expanded later to 15,000. It says it is disappointed with the French contribution and wants other European nations to offer more help too.

Israel's fresh incursion came five days after a UNbrokered ceasefire ended the month-long conflict.

Lebanese prime minister Fouad Siniora said the Israeli raid was a naked violation of the ceasefire.

The Israeli army said the raid was to prevent arms being delivered to Hezbollah by Iran and Syria.