UNESCO chief Irina Bokova appealed on Thursday to Syrian troops and jihadists to spare Palmyra from destruction as Islamic State group fighters advanced near the ancient site.
Syria's head of antiquities had urged international action to save Palmyra, saying the jihadists who have destroyed other historic sites had advanced to two kilometres (about a mile) from the remains of Palmyra.
Bokova, who was in Cairo for a two-day conference on protecting archeological sites, said "Palmyra must saved."
"It represents an irreplaceable treasure for the Syrian people, and the world," the head of the UN cultural agency said in a statement provided to AFP.
"I appeal to all parties in the conflict to protect Palmyra and prevent its destruction."
UNESCO describes Palmyra as a heritage site of "outstanding universal value".
The ancient city stood on a caravan route at the crossroads of several civilisations and its 1st and 2nd century temples and colonnaded streets mark a unique blend of Graeco-Roman and Persian influences.
Representatives of 10 Arab countries concluded a two-day meeting in Cairo on Thursday with a condemnation of the Islamic State group's destruction of ancient sites in Iraq.