Islamic State (Isis) radicals have destroyed a 2,000-year-old statue of a lion outside the museum in the Syrian city of Palmyra, the country’s antiquities director has said.

Maamoun Abdelkarim said the statue, known as the Lion of al-Lat, was an irreplaceable piece. “IS members on Saturday destroyed the Lion of al-Lat, which is a unique piece that is three metres [10ft] tall and weighs 15 tonnes,” Abdelkarim told AFP. “It’s the most serious crime they have committed against Palmyra’s heritage.”

The limestone statue was discovered in 1977 by a Polish archaeological mission at the temple of al-Lat, a pre-Islamic Arabian goddess, and dated back to the 1st century BC.

Abdelkarim said the statue had been covered with a metal plate and sandbags to protect it from fighting, “but we never imagined that IS would come to the town to destroy it.”

Isis captured Palmyra, a Unesco world heritage site, from government forces on 21 May, prompting international concern about the fate of the city’s antiquities.

So far the most famous sites have been left intact, though there have been reports that Isis has mined them. Most of the pieces in the city’s museum were evacuated by antiquities staff before Isis arrived. The group has blown up several historic Muslim graves in recent weeks.

On Thursday the group released photos showing its members in Aleppo destroying several statues from Palmyra they had caught being smuggled through the northern province.

“An IS checkpoint in Wilyat arrested a person transporting several statues from Palmyra,” the group said in an online statement. “The guilty party was taken to an Islamic court in the town of Minbej, where it was decided that the trafficker would be punished and the statues destroyed.”

The statement included photos showing several carved busts being destroyed with sledgehammers. Abdelkarim said the busts “appear to be eight statues stolen from the tombs in Palmyra. The destruction is worse than the theft because they cannot be recovered.”

Under Isis’s harsh interpretation of Islam, statues and grave markers are considered to be idolatrous. The group has destroyed countless antiquities and heritage sites in territory under its control in Syria and Iraq. The Guardian