About 2,500 Lebanese soldiers started on Thursday to deploy into southern Lebanon in a "first and initial phase", an army source said, marking the first time in decades that the Lebanese army has had a presence in the border region.
"The deployment started at 6.40 am on Thursday," he said.
Trucks loaded with tanks and armoured personnel carriers crossed a makeshift bridge in Qasimiya at the outskirts of southern port city of Tyre and headed to the village of Tebnine deep in the south.
Meanwhile, troops were transported by sea from Jiyeh to Tyre to speed up the operations because of the bad conditions of the roads from the month-long Israeli bombardment of Lebanon that began after Hezbollah's abduction of two Israeli soldiers on July 12.
An eventual 15,000 Lebanese troops are to be deployed with another 15,000 UN peacekeepers in the region that has been controlled by Hezbollah militia since Israel withdrew in May 2000.
The Lebanese forces are to "gather on main points: on the bridges of Qasimiya at the mouth of the Litani River, the Khardaleh bridge southwest of the town of Marjayun and in Hasbaya," the army source said.
The operation was expected to last three to four days, military sources said.
Earlier, the Israeli military said it had withdrawn its forces from southern Lebanon as part of a ceasefire that began on Monday.
An Israeli military spokeswoman said early Thursday that Israeli troops had begun handing over their positions to some 2,000 UN forces already operating in south Lebanon.
The handover would occur in phases according to the strength of the UN forces and the abilities of the Lebanese military to control the region, Israeli officials said.
Dan Huluz, chief of staff for the Israel Defence Forces, said the handover could be finished by the end of next week.
What remains to be seen, however, is whether the Lebanese army aims to disarm the Hezbollah militia.