* Yabroud gives government control from Damascus to Homs
* Rebels withdraw, lose vital cross-border supply line
* Battle intensifies to close border crossings to Lebanon
* Car bomb in Lebanon targets Hezbollah for Syria engagement
By Mariam Karouny and Stephen Kalin
BEIRUT, March 16 (Reuters) - Syrian forces backed by Hezbollah militants took full control of the town of Yabroud on Sunday after driving out rebels, helping President Bashar al-Assad secure the land route connecting the capital Damascus with Aleppo and the Mediterranean coast.
The fall of Yabroud, the last rebel bastion near the Lebanese border, could sever a vital insurgent supply line from Lebanon and consolidate government control over a swathe of territory from Damascus to the central city of Homs.
The army "restored security and stability to Yabroud...after eliminating a large number of terrorist mercenaries", the Syrian military said in a statement hailing the strategic victory.
A suicide bomber killed three people in a strike on a Hezbollah stronghold in Lebanon's Bekaa Valley on Sunday. Radical Sunni groups have pledged to attack the Shi'ite Muslim militant group in Lebanon until it withdraws from Syria.
A military source in Syria told Reuters that about 1,400 rebels from the Free Syrian Army, Ahrar al-Sham and other factions had fled Yabroud in the past two days. Another 1,000 militants from the al Qaeda-linked Nusra Front had stayed to fight government forces which had entered eastern districts of Yabroud and captured several hilltops.
"They fought a fierce battle and then from last night until the early hours of today, they all pulled out," he said.
The source said the militants had withdrawn to the nearby villages of Hosh Arab, Fleita and Rankos as well as Arsal, a Lebanese border town 20 km (13 miles) to the northwest.
Thousands of civilians fled Yabroud, a town of about 40,000 to 50,000 people, roughly 60 km (40 miles) north of Damascus, and the surrounding areas after it was bombed and shelled last month ahead of the government offensive.
The government has been making incremental gains along the land route and around Damascus and Aleppo in the past months, regaining the initiative in the three-year uprising-turned-civil war, which has killed more than 140,000 people.
Syria's Mediterranean coastal region is strategically vital for Assad because it is the heartland of his minority Alawite community, whose faith is an offshoot of Shi'ite Islam.
BATTLE TO CLOSE THE CROSSINGS
The military source said that in parallel to the capture of Yabroud, the army and air force had closed 14 of 18 crossings into Lebanon, where violence has spilled over in the past year.
"In the next few days, the battle will be over closing these remaining crossings," the source said.
Syrian and Lebanese television stations broadcasting from Yabroud said the military was targeting rebels in nearby villages. The anti-Assad Syrian Observatory for Human Rights monitoring group said it dropped barrel bombs on rebel-held Ras al-Maara, killing six people including two children
An influx of militants into Lebanon from Syria threatens to further destabilise the small Mediterranean country whose own 15-year civil war ended in 1990. The war in Syria has already heightened sectarian tensions between Shi'ite and Sunni Muslims, causing insecurity and political gridlock in Lebanon.
A local Lebanese official from Arsal told Al Arabiya television he wanted the Lebanese army to secure the border.
"We in Arsal are not ready to accept militants... The militants' battle is in Syria, not in Lebanon. Arsal will not be the place from which war is sparked inside Lebanon," he said.
A Lebanese security source told Reuters that Lebanese forces were confronting insurgents crossing the border from Syria, but in at least one incident, militants evaded an army checkpoint.
A field hospital in Arsal received the bodies of seven people killed and 100 others wounded in Syria, most of them Syrian nationals, according to Lebanon's National News Agency.
END OF YABROUD BATTLE
Hezbollah-operated Al Manar television broadcast scenes from Yabroud's main square where people walked around and talked in apparent safety. Soldiers replaced the three-star flag of the Syrian revolution with the government's two-star banner.
Footage from earlier in the day showed empty streets, shuttered shops and abandoned homes in a main thoroughfare. Heavy gunfire could be heard in the background.
The Observatory said fighters from Hezbollah, who helped seal off the frontier area with Lebanon, were now in charge of large parts of Yabroud. It said 19 Hezbollah fighters were killed. A funeral for one of the dead was held Lebanon's Tyre.
Abdelrahman said it was unclear where about 2,000 foreign fighters had ended up. "The Nusra Front had a lot of influence in the region, but their influence has now ended," he said.
The army was dismantling a large number of explosive devices planted by the rebels in Yabroud, Syrian state television said.
The military source said that among the rebel positions the army seized was the headquarters where the Nusra Front had held hostage 13 Greek Orthodox nuns for more than three months before their release last week in a rare prisoner swap.