BEIRUT (Reuters) - Syrian government forces launched an offensive to wrest back control of an historic Christian town north of Damascus on Monday, activists said.

In the past six days, the town of Maaloula has already changed hands three times between President Bashar al-Assad's forces and rebel groups, some of which are linked to al Qaeda.

Combatants say the intensity of fighting over the town is due to its strategic location near the road leading from Damascus to the central city of Homs.

But fighting in an area with such religious symbolism could increase anxieties among the Christian minority, who have watched sectarian violence between majority Sunni Muslims and the Alawite minority overshadow the revolt against Assad's rule.

The fighting near Maaloula, in the Qalamoun mountains north of the capital, threatens ancient Christian sites nestled in the hillsides that were a site of pilgrimage for Christians and Muslims alike.

The Britain-based Observatory, which opposes Assad, said that troops and militia loyal to the president re-entered Maaloula early Saturday but withdrew in the evening when rebels brought in reinforcements.

Retreating government forces continued to shell and clash with insurgents on the outskirts of Maaloula on Sunday and Monday, said Rami Abdelrahman, head of the Observatory, though violence inside the town abated on Monday morning.

Maaloula has several churches and important monasteries as well as the Greek Orthodox nunnery Mar Thecla, visited by many Christians and Muslims who are drawn by its reputation as a holy place where the sick would be miraculously healed.

A sizeable number of the inhabitants of Maaloula, as well as Sarkha and Jabaadeen, two nearby Sunni towns, still speak Aramaic, the language of Christ.

Abdelrahman said 18 rebel fighters were killed and over 100 injured during Saturday's fighting. He could not confirm the extent of casualties among government forces.

Restrictions by Syrian authorities on independent media make it difficult to verify these accounts.

PILLAGING DENIED

Most residents had fled Maaloula when fighting erupted last Wednesday around a roadblock manned by government fighters.

Rebels entered the town later that day but withdrew on Thursday. The Mother Superior at Mar Thecla denied reports circulated by pro-government groups that rebels had pillaged Christian holy sites.

Among opposition forces who took control of the town on Saturday were the al Qaeda-linked Nusra Front, according to the Syrian Observatory for Human Rights.

Members of that group uploaded a video statement to YouTube on Sunday renouncing any intention to occupy Maaloula.

Surrounded by about ten rebels wearing balaclavas and carrying assault weapons, a man says the fighters had aimed to take over a roadblock near Maaloula last week and only entered the town to defend it from government attacks.

"Soon we will withdraw from this city not out of fear but to leave its homes to their owners. They were not our target. Our target was mainly military," he said.

The video ends with an interview of two elderly women wearing the black garb of Christian nuns. One of the women says that the rebels treated them "very well", but the rest of her comment was droned out by the near constant sound of shelling in the background.

Syria's Christian community is wary of the rising power of Islamist groups within the rebel movement but has remained largely on the sidelines since 2011, when peaceful demonstrators began protesting four decades of rule by the Assad family.

Christians make up roughly 10 percent of Syria's population. A small percentage so far have taken up arms in the civil war that broadly pits minorities, in particular Assad's Alawite sect, an offshoot of Shi'ite Islam, against the Sunni Muslim majority.