Krak des Chevaliers, built between 1142 and 1271 and considered one of the best preserved Crusader castles in existence, has already sustained damage from previous fighting between militants and army forces during Syria's three-year conflict.

"The army entered Al-Hosn and took two districts of the village. It is bombarding areas around the Krak des Chevaliers to take control of the castle," the official said on Wednesday, speaking on condition of anonymity.

State news agency SANA meanwhile said the army had carried out an ambush of opposition forces west of the nearby town of Zara, which it captured on March 8.

The army was also engaged in continuing clashes in the Qalamoun region, along the border with Lebanon, where it captured the rebel bastion of Yabroud on Sunday.

The Syrian Observatory for Human Rights, a Britain-based NGO, reported fierce fighting between army forces and militants at a checkpoint near the town of Rankus, south of Yabroud.

It said government troops backed by Lebanon's Hezbollah and pro-army militia were also fighting terrorists around the villages of Bkhaa and Jobeh in Qalamoun region.

BA/BA