The ancient site of Hasankeyf is in a spectacular setting
Insurers have suspended their support for a controversial dam project in southeastern Turkey amid concern about its environmental and cultural impact.
Export credit insurers in Austria, Germany and Switzerland said on Tuesday they had told suppliers to suspend work on the Ilisu dam on the Tigris river.
They are giving Ankara 180 days to meet standards set by the World Bank.
The ancient Hasankeyf fortress is in the area that would be flooded and more than 50,000 people would have to move.
The hydroelectric project near Turkey's borders with Syria and Iraq is part of a scheme to develop the mainly Kurdish region, which has suffered for decades from poverty, neglect and conflict.
Environmentalists say the dam would destroy archaeological treasures, including Roman remains.
The dam consortium plans to create a culture park on the edge of the reservoir and transfer key monuments from Hasankeyf there.
In a joint statement, the project's Austrian, German and Swiss underwriters said: "There was significant progress in recent weeks to implement the project according to World Bank standards.
"However, the progress is not enough to approve building measures."
The statement came from the Swiss state-run Export Risk Insurance, Euler Hermes of Germany and Austria's Oesterreichische Kontrollbank.
The 1.2bn euro (£1.1bn; $1.7bn) Ilisu dam project would flood more than 300 sq km (116 sq miles) of land to create the second largest reservoir in the country.
The aim is to generate electricity to feed rapidly rising demand and fuel Turkey's economic development.