Fears is growing for the lives of 40 Syrian workers employed in Palmyra by the country's antiquities department after the Islamic State (Isis) beheaded famed 82-year-old retired archeologist of the Unesco World Heritage site, Khaled al-Asaad.

Syrian antiquities director Maamoun Abdulkarim told IBTimes UK Asaad's son and current chief for Palmyra ruins, Walid, has gone into hiding along with other 40 people in the ancient city, which was captured by IS from government forces in May.

"They don't go to the ruins or the museum anymore. They don't publicly declare to be employees, they behave like all the other Palmyra inhabitants. But they are still my colleagues, although communication is poor," the Damascus-based archaeologist said.

I was born in Palmyra, passed my life here: how can I leave Palmyra in this terrible situation? I will resist here - Khaled Asaad, Palmyra\'s ex antiquities director

The jihadist group decapitated Asaad and hung his mutilated body on a column in a main square in the city's well-preserved Greco-Roman ruins, Abdulkarim said.

However, a photo circulated online showing the body of the old archeologist tied to a lamp post with a sign attached to the body accusing him of being a loyalist to the regime of Bashar al-Assad and representing Syria abroad with "infidels". It also accused him of being director of Palmyra's idols.

Abdulkarim said he begged Asaad to leave Palmyra after it was captured by IS. "I told him to come to Damascus because staying in Palmyra was too dangerous, but he refused. He told me: 'I was born in Palmyra, passed my life here: how can I leave Palmyra in this terrible situation? I will resist here.'"

Asaad was praised as one of the father of Syrian archeology in Palmyra, spending 54 years as head of antiquities. AFP reported that Asaad spoke and read Palmyrene, and was often asked to determine whether stolen statues were real or fake. He also knew Aramaic and published several scholarly works about Palmyra. According to Sana, Syrian state agency, and the UK-based Syrian Observatory for Human Rights (SOHR), Asaad was beheaded in front of dozens of people in a square outside Palmyra's museum.

IS detained him one month ago along with his son Walid, who was later released, about alleged "stores of gold" in the city. But Abdulkarim categorically denied that any gold ever existed in the town. "We had a lot of Greco-Roman statues which we transferred to Damascus, but we never had gold and we don't have it now," he said.

'Shocking and barbaric'

"It's shocking and barbaric how they managed to kill a person like him who spent 82 years in Palmyra for their propaganda and sick ideals," Abdulkarim added.

The jihadist group seized Palmyra in May, raising fears it would destroy the 2,000-year-old Unesco world heritage site. In a recent development, the extremist group laid mines around the archeological site and destroyed a number of statues from the city. IS also demolished two ancient Muslim shrines deeply revered by the local population and the famous statue of a lion outside the town's museum. Most of the pieces have been evacuated by Abdulkarim's staff before IS arrived.

The ruins have not suffered any damage, according to Abdulkarim, because of divisions between IS foreign and Syrian fighters, who want to preserve the ancient heritage. "The museum has shut down and IS militants are refusing entry to our stuff," he said.

The UN describes Palmyra as a site of "outstanding value". An ancient metropolis and a caravan hub of several civilisations, Palmyra is full of precious sculptures and artefacts. It is renowned for its urbanism – a unique mix of Roman architecture with Greek-Persian and Babylonian influences. It is admired for its famous colonnaded main street and admired in particular for the temple of Baal, considered one of the most important cultural monuments of the entire region.