BEIRUT -- Khaled Asaad was a respected scholar who devoted more than five decades of his life to preserving the majestic, 2,000-year-old ruins of Palmyra, a city in the Syrian desert.

On Tuesday, Islamic State extremists beheaded the former chief of antiquities in the city and left his body hanging in public for terrified residents to view, according to the official Syrian Arab News Agency.

The killing of Asaad, confirmed by Syrian activists, marks not just another attack by the Islamist militants on the region's vast archaeological heritage but also an assault on those who look after it.

The archaeologist, whose age was given by various sources as between 81 and 83, was killed after he refused to divulge information on "specific archaeological treasures," according to SANA.

The government's antiquities chief, Maamoun Abdulkarim, told the news agency that the militants crucified Asaad "on colonnades in central Palmyra."

However, a photograph posted on Twitter purports to show Asaad's body hanging from a street lamppost. A sign on the corpse described the killing as punishment for working with "idols," an apparent reference to the area's Roman-era artifacts.

The Islamic State captured Palmyra in May, prompting fears that the group would destroy the UNESCO World Heritage site, about 150 miles northeast of the capital, Damascus. Syrian activists say the group has killed hundreds of residents in the city, which had a pre-civil war population of about 200,000.

Last month, the Islamic State, also known as ISIS or ISIL, released a video showing child soldiers summarily executing 25 government troops in the city's Roman amphitheater. In the video, the boys are shown firing pistols into the heads of the soldiers, who are kneeling with their hands tied behind their backs.

In addition to perpetrating mass murder, the Islamic State has carried out sweeping anti-idolatry campaigns, laying waste to vast amounts of precious artifacts in the areas of Syria and Iraq under its control.

The group uses extremist interpretations of Sunni Islam to justify the destruction, which often targets pre-Islamic artifacts and other symbols of multiculturalism viewed as idolatry.

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Asaad was considered a pioneer in Syrian archaeological circles. Among other accomplishments, he authored volumes of scholarly works on Palmyra, and he teamed with Western archaeological missions to excavate and research the city's ancient tombs and temples.