A satellite image shows the main building of the ancient Temple of Bel in the Syrian city of Palmyra has been destroyed, a United Nations agency said.
The image was taken a day after a massive explosion was set off near the 2,000-year-old temple in the city occupied by Islamic State (IS) militants.
Earlier, Maamoun Abdulkarim, head of the antiquities and museums department in Damascus, had said there was conflicting information about the temple, one of the most prominent structures in a sprawling Roman-era complex, because eyewitnesses were unable to approach the site.
But Einar Bjorgo, manager of Geneva-based UN satellite analysts UNOSAT, said a satellite image "unfortunately shows the destruction of the temple's main building as well as a row of columns in its immediate vicinity".
UNOSAT based its findings after comparing the image with one taken on August 27 which showed the main building and columns still intact
Mr Bjorgo said the images were important so the UN cultural agency UNESCO could have "objective information" about the situation in Palmyra, which UNESCO has designated a world heritage site.
IS, which captured Palmyra from forces loyal to President Bashar Assad in May, destroyed the smaller Temple of Baalshamin in the complex last week and posted images of the destruction days later. UNESCO condemned the act as a war crime.
Activists, including a Palmyra resident, said earlier that an IS bombing extensively damaged the 2,000-year old temple on Sunday. The resident described a massive explosion, adding that he saw pictures of the damage but could not get near the site.
An IS operative told The Associated Press that militants detonated explosives near the temple, without elaborating on how much of it was damaged.
Residents in Palmyra told the official Syrian state news agency IS militants destroyed large parts of the temple and booby trapped other parts of it, expressing concern that they plan to destroy the rest soon.
Amr al-Azm, a former Syrian antiquities official who now is a professor at Shawnee State University in Ohio, in the US, said he believed a very large amount of explosives was used and the damage to the Temple of Bel was likely extensive.
"This is the most devastating act yet in my opinion. It truly demonstrates ISIS's ability to act with impunity and the impotence of the international community to stop them," he said, using an alternative name for the group.
Earlier this month, relatives and witnesses said IS militants had beheaded Khaled al-Asaad, an 81-year-old antiquities scholar who devoted his life to understanding Palmyra.
IS, which has imposed a violent interpretation of Islamic law across its self-declared "caliphate" straddling Syria and Iraq, says such ancient relics promote idolatry.
It already has blown up several sites in neighbouring Iraq, and it is also believed to be selling looted antiquities.
The Temple of Bel, dating back to 32 AD, shows a unique merging of ancient Near Eastern and Greco-Roman architecture.
It is dedicated to the Semitic god Bel and is considered one of the most important religious buildings of the first century. The temple consisted of a central shrine within a colonnaded courtyard with a large gateway, within a complex that has other ruins, including an amphitheatre and some tombs.
It stood out among the ruins not far from the colonnades of Palmyra, which is known by Syrians as the "Bride of the Desert".
Palmyra was an important caravan city of the Roman Empire, linking it to India, China, and Persia. Before the outbreak of Syria's conflict in March 2011, the UNESCO site was one of the most popular tourist attractions in the Middle East.
UNESCO chief Irina Bokova said IS militants in Syria committed an "intolerable crime against civilisation" by destroying the Temple of Bel.
She said that her agency will try to protect "all that can be saved" in the group's reach.