"Army units have begun deploying," a senior military official told AFP.
The first phase of the promised deployment to the long time Hezbollah bastion in southern Lebanon involves 2,000 government troops and comes on the fourth day of a UN-brokered ceasefire to bring a halt to a month of bloodshed.
The operation is expected to last three to four days, with troops heading south across the strategic Litani river, an area that has borne the brunt of Israel's massive offensive that began on July 12.
The troop move, which will involve a total of 15,000 men, was approved by the Lebanese cabinet on Wednesday and is expected to be bolstered by the reinforcement of a UN peacekeeping force in the south.
Israel also announced yesterday that it had begun pulling back its troops from parts of the south and handed over control to UN peacekeepers.
UN to form peacekeeping force
Meanwhile countries willing to commit troops to a peacekeeping mission in southern Lebanon were due to meet at the United Nations, in talks set to focus on the rules of engagement.
UN Secretary General Kofi Annan's spokesman Stephane Dujarric said the talks would flesh out details on the force's mandate as agreed under Security Council Resolution 1701 on Friday.
The resolution gives a mandate for UNIFIL to swell from its current level of 1,990 troops to 15,000.
The UN is counting on France to deliver the backbone of the force, designed to help the Lebanese government assert its authority over an area long dominated by the Hezbollah Shiite militia.
France signalled it was ready to take command of an enlarged UN force until February.
"France has been in UNIFIL (the UN interim force in Lebanon) since 1978 and we are in command today," French Defence Minister Michele Alliot-Marie said on French television channel France 2.
"We are going to continue to maintain this command, we are ready to do so until next February, including for an enlarged UNIFIL."
The UN said it hoped an initial deployment of more than 3,000 troops for the strengthened force could be in place within two weeks to shore up the fragile truce between Israel and Hezbollah.
The French defence minister declined to say how many extra troops France would be prepared to send, and warned that the mission was not without risks due to the as yet "unclear" nature of the UN mandate.
"When a force is sent without its mission being very precise, without its means being adapted or sufficiently large, it could turn into a catastrophe, including for the troops that we send," she said.
She also stressed: "It is indispensable that there be the maximum of European countries and Muslim countries' representatives" involved in the enlarged force.
"It must not be that at any moment the impression could be had that this mission is going to be one of the Western world against the Muslim world," Ms Alliot-Marie said.
She said that so far Malaysia, Indonesia, Brunei and Australia had said that they were ready in principle to help make up the enlarged force. Turkey was also considering whether to take part.
France, which has historical links to Lebanon, penned the UN resolution together with the US.
Lebanon was ruled by a League of Nations mandate under French administration from 1920, before it became independent in 1943.
Progress expected
Britain, meanwhile, said it was expecting rapid progress on the ground after the talks, with Ambassador to the UN, Emyr Jones Parry saying that fixing the rules of engagement should be the spur for countries to commit troops.
"I think tomorrow (Thursday) you will see an early agreement to what the mandate implementation should be," he told journalists.
He added that while London lacked the military resources to play a major role in the force, it would at least offer logistical support.
He was upbeat about the ceasefire holding on the ground.
"The situation as I understand on the Blue Line this morning is stable and OK, so there are positive signs out there.
"We're seeing on the ground today the handing over of some of the villages to the Lebanese forces. I expect that trend to continue, and what we have to do is maximise the replenishment, renewal, reinforcement of (UN peacekeeping force) UNIFIL," he said.
Lebanese troops deployed
As foreign powers scrambled to strengthen UNIFIL, the Lebanese government decided to start the deployment of 15,000 of its troops to southern Lebanon as Israel prepared to withdraw its troops.
Lebanese Prime Minister Fuad Siniora said the deployment of government troops to Hezbollah's bastion in the south would end a "mentality of statelets" and make the army the only armed force in the country.
The deployment, which was due to begin at 6 am local time (0300 GMT) on Thursday, would "assert state authority" and ensure there would be "no armed presence outside state authority," Mr Siniora said.
In a televised address after the cabinet approved the deployment of 15,000 troops to the south in line with a UN truce resolution MM Mr Siniora said: "There will be no more mentality of statelets, factional programmes.
"There will be a single state ... with the sole decision-making power, there will be no dual authority.
"Nobody, whether inside or outside the country, has the right to lead the people and the nation where he wants, and then have everybody else follow him or be considered separatist ... or doubted in their nationalist and Arab loyalty," he said.
He was apparently alluding to Hezbollah and its supporter Syria which on Wednesday accused anti-Damascus Lebanese politicians like the prime minister of being "made in Israel."
After Israel ended a 22-year occupation of south Lebanon in 2000, the region was the preserve of Hezbollah fighters until Israeli troops returned in response to the Shiite militant group's capture of two soldiers in a deadly cross-border raid on July 12.
Mr Siniora said his government remained determined to secure the release of Lebanese detained in Israel and free the disputed Shebaa Farms border territory from Israeli occupation.