Syrian activists say Islamic State (IS) militants have destroyed a nearly 2,000-year-old arch in the ancient city of Palmyra.
It is the latest historical site to be destroyed by IS in the territory it controls in Iraq and Syria.
The Arch of Triumph was one of the most famous sites in Palmyra, which the IS extremist group captured in May.
The Syrian Observatory for Human Rights monitoring group said the militants destroyed the arch on October 4 because of ornaments on its columns the group considered un-Islamic.
But the Britain-based group said the militants left the colonnades in place.
The monumental arch sat on top of the famous colonnaded streets of the ancient city, which linked the Roman Empire to Persia.
UNESCO Director-General Irina Bokova said IS "extremists are terrified by history and culture," and that the UN's scientific and cultural body would make every effort to ensure that the perpetrators of the destruction were brought to justice.