A group of ISIL fighters and their families surrendered their enclave on the Lebanon-Syria border and left for an area in eastern Syria held by the extremists on Monday, Syrian state television showed.
Under the terms of a truce, ISIL agreed to surrender its enclave after a week-long offensive by the Lebanese army on one front and the Syrian army and Lebanon's Shiite Hizbollah group on another.
It was the first time extremist group publicly agreed to a forced evacuation from territory it held in Syria, and will put an end to any Sunni militant presence on the border - an important goal for Lebanon and the Hizbollah.
Nearly two dozen buses and 11 ambulances transported the convoy of ISIL militants and their families from the area straddling the Syria-Lebanon border toward the ISIL-held town of Boukamal in eastern Syria.
A total of 600 people will leave in the convoy, Syria's state-run Al Ikhbariya television station reported.
Ambulances carried 25 injured ISIL fighters from the area, according to the Central Military Centre, a media outlet run by Hizbollah.
On Monday, the Lebanese army hosted dozens of local and international media to show off areas on the outskirts of the northern city of Ras Baalbek that it had recently recaptured from ISIL. An army spokesman said there are about 20 square kilometres on the Lebanese border with Syria where ISIL fighters remain.
It was unclear whether any of those fighters had begun or would withdraw to Syria in hopes of being part of the deal with the Syrian government.
The Lebanese government declared a ceasefire with ISIL on Sunday that remains largely in effect, though shelling by the Lebanese military against what an officer said was an ISIL-held area was observed.
The army has said the fight against ISIL could restart at any time.
ISIL agreed a ceasefire on Sunday after losing much of its mountainous enclave straddling the border, paving the way for its evacuation.
Lebanese officials and Hizbollah say the evacuation is a sign of surrender by the extremist group.
"We do not bargain. We are in the position of the victor and are imposing conditions," Lebanese Internal Security General Abbas Ibrahim said on Sunday.
Hizbollah has been a close ally of Syrian president Bashar Al Assad through Syria's six-year civil war.
The Lebanese army - which launched a military campaign to drive the militants from the rugged mountainous area along its border with Syria nearly a week ago - said its offensive against ISIL did not involve coordination with Hizbollah or the Syrian army. About 5,000 Lebanese soldiers took part in the offensive.
A senior Lebanese military official said a number of militants were also leaving from the Lebanese side of the border, to be transferred with the Syrian convoy. The official, who spoke on condition of anonymity, did not have a number for militants leaving Lebanon.
A commander in the pro-Assad military alliance said Syria and Hizbollah agreed to evacuate ISIL fighters in order to avert a bloody war of attrition.
ISIL fighters were sheltering among civilians and to complete the offensive would have involved great bloodshed, the commander added. "Every battle that ends with negotiation or surrender is a victory," the commander said.
Under the agreement, the militants are to move out of their positions to a point on the Syrian side of the border before their transport to Boukamal in eastern Syria, a Lebanese security source said.
Syrian state-run TV reported on Monday that the group was burning its machinery and headquarters.
A witness in Syria at the position where buses were gathering to receive the extremist fighters said black smoke was visible in the hills and Syrian army and Hizbollah vehicles were present.
The transfer of the militants is part of a deal that came into effect following Hizbollah-led negotiations to determine the fate of nine Lebanese soldiers captured by ISIL when the militants overran the Lebanese town of Arsal in 2014.
A senior Lebanese security official said late on Sunday the soldiers were almost certainly dead after recovering six bodies and digging for two others in areas previously held by ISIL.
Earlier this month, two other pockets straddling the border were recaptured by Lebanon and Syria after other militant groups accepted similar evacuation deals.
Those agreements were prompted by a brief Hizbollah offensive that began at the end of July against militants of the group formerly known as Nusra Front, which was Al Qaeda's official partner in Syria until last year.
Hizbollah has maintained a strong presence in the parts of Syria near the border with Lebanon for years, helping Mr Al Assad to recapture several rebel-held towns and villages there.
The threat to Lebanese territory from rebel and militant groups in Syria was evident in the 2014 attack on Arsal. Suicide bomb attacks struck a predominately Shiite area in south Beirut, where Hizbollah is widely supported, in November 2015.
Inside Syria, ISIL is retreating on all fronts, losing territory both to the Syrian army and its allies, and to an alliance of Kurdish and Arab militias backed by a US-led coalition.
