Gen. Michel Suleiman told about 500 soldiers that the army won't allow any attacks from Lebanon that could undermine the cease-fire — an apparent reference to rockets Hezbollah launched at Israel from the south in 34 days of fighting that ended Aug. 14.
"Stay vigilant to uphold the law and deter whoever undermines the course of security and stability," Suleiman said.
He said that although his army is no match for Israel, it would fight if necessary.
"I call upon you to confront the Israeli aggressions and violations with whatever meager capabilities that are available," he said.
The United Nations-brokered cease-fire supports the Lebanese military in reasserting control over the south — including areas last held by the national army 30 years ago.
The Lebanese troops are supported by a beefed-up U.N. peacekeeping mission as they move to extend Lebanese authority over the entire south.
Lebanese troops were expected to fan out through the areas newly vacated by Israel beginning Monday.
But Israeli forces' continued presence in part of the border village of Ghajar, and their plans to continue patrolling Lebanese airspace, are potential sources of friction between the neighbors.
An army spokesman said Lebanese army deployment in the south has exceeded the minimum of 15,000 troops required by the U.N. cease-fire resolution. The spokesman requested anonymity in compliance with military regulations.
The United Nations Interim Force in Lebanon called Israel's pullout from nearly all of south Lebanon "significant progress." But both the Lebanese government and Hezbollah dismissed the withdrawal Sunday as "incomplete" and demanded Israel stop what they called its violations of Lebanon's airspace, sea and land.
Parliamentary Speaker Nabih Berri, a close ally of Hezbollah, warned that guerrilla attacks could resume if Israel did not fulfill the U.N. cease-fire resolution and all Lebanese territory is regained.
"Our right of resistance is always there," he told As-Safir newspaper on Monday.
Senior Hezbollah official Sheik Hassan Ezzeddine warned that the Islamic militant group would resume attacks against Israel if it breached the U.N. cease-fire.
UNIFIL confirmed in a statement Sunday that Israel had withdrawn from the entire south except Ghajar.
The pre-dawn pullout Sunday put a formal end to a nearly three-month incursion into Lebanon that began after Hezbollah guerrillas captured two Israeli soldiers and killed three others in a July 12 cross-border raid.
It clears the way for the full deployment of UNIFIL's 15,000 soldiers, who will police the border with Lebanese troops.
Israel wants Lebanon to keep Hezbollah out of the south and disarm it, but Beirut has indicated it would not actively seek Hezbollah's weapons. The militant group said it would disarm only when a strong central government was in place.