According to the British-based Syrian Observatory for Human Rights, the temple of Baalshamin in the ancient Syrian city of Palmyra was blown up by ISIS militants on Sunday.
“(ISIS) placed a large quantity of explosives in the temple of Baalshamin today and then blew it up causing much damage to the temple," Syrian antiquities chief Maamoun Abdulkarim told the AFP news agency.
"The cella (inner area of the temple) was destroyed and the columns around collapsed," he added.
Palmyra is a 2,000-year-old antique city home to Roman era ruins, which was added to the UNESCO World Cultural Heritage List in 1980.
ISIS, which is known for destroying all historical sites in neighbouring Iraq, started attacks on the central Homs province May, raising alarm both in Syria and abroad.
Earlier in June, ISIS also blew up two ancient shrines that were considered pagan structures by the militants.
ISIS, which captured Palmyra in May, currently controls swathes of territory larger than Britain, extending from eastern Syria to western Iraq.