Unveiling its watch list for 2014, the World Monuments Fund (WMF) warned that conflict, catastrophe, lack of resources, development pressures and loss of cultural traditions threaten sites in 41 countries.
For the first time, all heritage sites in Syria have been included on the list, which is normally dedicated to individual sites.
Syria has some of the oldest sites on the list. The citadel in Aleppo, the northern Syrian city torn apart by a 30-month civil war war, dates back to the early Bronze Age, 3300-2200 BC.
"In Syria, the ongoing civil conflict has a terrible toll on monuments and sites which continues. We placed the entire country of Syria in the watch list," said WMF president Bonnie Burnham.
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"In the spirit of solidarity we also placed the cultural heritage of Mali on the watch list... A lot of damage has been done," she added.
The United Nations says more than 100,000 people have been killed in the conflict in Syria.
Burnham said WMF would do "everything we can" to help those sites on the list, compiled every other year, over the next 48 months.
WMF says it seeks to raise awareness of the threats, and to galvanise the skills and resources of the global community for a time when it is safe to return.
Since it was set up in 1996, WMF has included more than 740 sites on its watch lists, which has resulted in $300 million being invested in their preservation.