BEIRUT — Islamic State militants have destroyed a temple at Syria’s ancient ruins of Palmyra, activists said Sunday, realizing the worst fears archaeologists had for the 2,000-year-old Roman-era city after the extremists seized it and beheaded a local scholar.

Palmyra, one of the Middle East’s most spectacular archaeological sites and a UNESCO World Heritage site, sits near the modern Syrian city of the same name. Activists said the militants used explosives to blow up the Baalshamin Temple on its grounds, the blast so powerful it also damaged some of the Roman columns around it.

The Sunni extremists, who have imposed a violent interpretation of Islamic law across their self-declared “caliphate” in territory they control in Syria and Iraq, claim ancient relics promote idolatry and say they are destroying them as part of their purge of paganism. However, they are also believed to sell off looted antiquities, bringing in significant sums of cash.

The Baalshamin Temple is about 550 yards from Palmyra’s famous amphitheater where the group killed more than 20 Syrian soldiers after they captured the historic town in May. The temple dates to the first century and is dedicated to the Phoenician god of storms and fertilizing rains.

The head of UNESCO, Irina Bokova, said Friday that Islamic State extremists in Syria and Iraq are engaged in the “most brutal, systematic” destruction of ancient sites since World War II – a stark warning that came hours after militants demolished the St. Elian Monastery, which housed a fifth-century tomb and served as a major pilgrimage site. The monastery was in the town of Qaryatain in central Syria.

News of the destruction comes after relatives and witnesses said Wednesday that Khaled al-Asaad, an 81-year-old antiquities scholar who devoted his life to understanding Palmyra, was beheaded by Islamic State militants, his bloodied body hung on a pole.

Meanwhile in Iraq, at least 23 soldiers and government-allied militiamen were killed Sunday in an attack by Islamic State militants in the turbulent Anbar province west of Baghdad, Iraqi military and police officials said, in the second heavy death toll suffered by the Iraqi military and its allies in recent days in the vast Sunni region.

The officials said Sunday’s attack, which killed 17 soldiers and six Sunni militia fighters, happened in the rural district of Jaramshah, north of Anbar’s provincial capital, Ramadi.