Islamic State (IS) militants have demolished the ancient Christian monastery of Mar Elian in the central Syrian town of al-Qaryatain.
The militants had also moved Christians taken captive in the town to their stronghold of Raqqa, according to a UK-based monitoring group.
IS captured al-Qaryatain from government forces some two weeks ago.
Separately, at least four people have died in an Israeli strike on a Syrian-held section of the Golan Heights.
Israel has carried out a wave of strikes in the area, which lies in south-western Syria, after rockets fired from Syria struck its territory on Thursday. The rockets set fire to scrubland but did not cause any casualties.
Israel’s military has accused Palestinian militants from the Islamic Jihad group of firing the rockets, while Prime Minister Benjamin Netanyahu said the attack had been ordered by Iran.
Islamic State militants in al-Qaryatain, in Homs province, reportedly used bulldozers to demolish the Mar Elian monastery. It was founded more than 1,500 years ago.
IS has also transferred more than 100 captives – including Christians seized when they overran al-Qaryatain – to Raqqa, according to the Syrian Observatory for Human Rights (SOHR), a group that monitors the conflict using a network of contacts in Syria.
The captives include Jacques Mourad, a prominent local priest who had been working at the Mar Elian monastery.
IS regards Christians as infidels. The threat of violence and persecution from the militants has forced many Christian communities from their homes in Syria and northern Iraq.
Al-Qaryatain was captured in the militants’ first major offensive since May, when they seized the historic town of Palmyra, famed for its Roman-style ruins.
More than 230,000 Syrians have died in the civil war, which began after anti-government protests in March 2011.
Rebel groups that originally fought against the government of President Bashar al-Assad have also been battling each other in an increasingly complex and bloody conflict.