Islamic State militants have destroyed a landmark ancient Roman monument and parts of the theatre in Syria's historic town of Palmyra, the government and opposition monitoring groups said.
Maamoun Abdulkarim, the head of Syria's antiquities department, said the militants destroyed the facade of the second-century theatre along with the Tetrapylon, a cubic-shaped Roman monument in the middle of the colonnade road that leads to the theatre.
Mr Abdulkarim said reports of the destruction first trickled out of the IS-held town late in December, but satellite images of the damage were only available late on Thursday, confirming the destruction.
The imagery, provided by the US-based American Schools of Oriental Research, show significant damage to the Tetrapylon and the theatre. The ASOR said the damage was probably caused by intentional destruction by IS.
Mr Abdulkarim said only two of the 16 columns of the Tetrapylon remain standing. The stage backdrop has sustained damage, according to ASOR.
State-run news agency Sana reported the damage and Syrian opposition monitors confirmed it but gave no immediate details.
The extremists recaptured the ancient town in December from government troops - nine months after IS was expelled in a Russia-backed offensive.
During their first stay, from May 2015 until May 2016, IS destroyed ancient temples including the Temple of Bel, which dated back to AD 32, and the Temple of Baalshamin, a structure of stone blocks several storeys high fronted by six towering columns.
The militants also blew up the Arch of Triumph, which was built under Roman emperor Septimius Severus between AD 193 and AD 211.
A Unesco world heritage site, Palmyra boasts 2,000-year-old towering Roman-era colonnades and priceless artefacts. Syrians affectionately refer to it as the "Bride of the Desert".
The extremists have destroyed ancient sites across their self-styled Islamic caliphate in Syria and Iraq, viewing them as monuments to idolatry.
A desert oasis surrounded by palm trees in central Syria, Palmyra is also a strategic crossroads linking the Syrian capital, Damascus, with the country's east and neighbouring Iraq.
Located 155 miles east of Damascus, the city was once home to 65,000 people before the Syrian civil war began.
Most Palmyra residents did not return after it was retaken by the government, and activists estimated the city is now home to a few hundred families.
Many of them tried to flee as IS recaptured the city in December.
On Thursday, reports emerged that the militant group killed 12 captives it held in Palmyra, some of them beheaded in the Roman theatre.
Meanwhile, Unesco said about a third of the ancient city of Aleppo has been destroyed during the war in Syria.
The United Nations cultural organisation conducted an emergency mission from Monday to Thursday to assess damage at the World Heritage Site and reported "extensive damage" at the Great Umayyad Mosque, the Citadel and other historic buildings.
Unesco said "60% of the old city of Aleppo has been severely damaged, with 30% totally destroyed".
The group's envoys met Aleppo council members and non-governmental organisations and proposed that the ancient city should be declared an "emergency zone".
Pro-government forces recaptured Aleppo in December, ending rebels' four-year hold on parts of what was once Syria's largest and most important city.