Nearly 300 cultural heritage sites have been destroyed, damaged and looted in Syria since its conflict broke out in 2011, the UN said Tuesday in a report citing satellite evidence.

Among the areas exposed to major damage were UNESCO world heritage sites such as Aleppo, where settlements have been in place for 7,000 years, and the fabled desert Greco-Roman oasis of Palmyra.

"Looting, destruction from aerial bombardment and other explosions, as well as infrastructure construction at cultural sites significantly threatens the heritage to future generations of these historic structures and objects," the UN said in a statement.

The report focused on 18 areas, of which six are UNESCO-listed: the Old City of Aleppo; Bosra; Damascus, the Dead Cities of northern Syria; Crac des Chevaliers and Palmyra.

Detailed analysis of satellite imagery of 290 locations at these sites showed 24 of them had been destroyed, 104 severely damaged, 85 moderately damaged and 77 possibly damaged.

The United Nations said the report was "alarming testimony of the ongoing damage that is happening to Syria's vast cultural heritage" and called for efforts to scale up their protection.

The satellite images were put together by UNOSAT, a Geneva-based UN institute.

"It is very sad for Syria as well as the world that this is happening," said UNOSAT director Einar Bjorgo.

"Humankind is losing hundreds and thousands of years of heritage," he told AFP.

"Perhaps some of it can be rebuilt, but what is looted may be lost, unless it resurfaces and is given back."