The head of the UN cultural agency on Tuesday expressed her deep shock at the damage to World Heritage sites in Syria and reiterated her call for an immediate end to such destruction, a UN spokesman told reporters here.

Irina Bokova, "the Director-General of the UN Educational, Scientific and Cultural Organization (UNESCO), has said on Tuesday she was deeply shocked at news of further destruction to cultural heritage in Syria, particularly reports of damage to the Crac des Chevaliers, a World Heritage site," said Martin Nesirky, spokesperson for UN secretary-general at the daily briefing.

"Bokova called on the perpetrators to cease the destruction immediately and urged all parties to the conflict to safeguard the site, along with all of Syria's cultural property," Nesirky said.

The Crac des Chevaliers is among six sites in Syria recently inscribed to the UNESCO List of World Heritage in Danger and is considered an outstanding example of the region's fortified architecture constructed during the Crusades between the 11th and 13th centuries.

According to several videos posted online on Saturday, at least one air strike on Friday against the Crusader castle in central Homs province, where fighting is raging between government troops and rebel forces, has damaged one of the fortress's towers,

Bokova also reminded all parties involved in the Syrian conflict of their legal obligations under the 1954 Hague Convention for the Protection of Cultural Property in the Event of Armed Conflict, to which Syria is a signatory and which enjoins High Contracting Parties, to refrain from any act of hostility directed against cultural property.

According to a statement issued on Tuesday by UNESCO, the agency stands prepared to cooperate with all parties concerned in deploying "all possible efforts" to protect Syria's cultural monuments to the extent allowed by the volatile security situation.