With chances of finding more survivors growing more remote, the toll in both countries from Monday's earthquake and major aftershocks rose above 33,000 and looked set to keep growing. It was the deadliest quake in Turkey since 1939.

In one of the worst hit cities, Antakya in southern Turkey, residents and aid workers who came from other cities cited worsening security conditions, with widespread accounts of businesses and collapsed homes being robbed. President Tayyip Erdogan said the government will deal firmly with looters.

In Syria, the disaster hit hardest in the rebel-held northwest, leaving homeless yet again many people who had already been displaced several times by a decade-old civil war. The region has received little aid compared to government-held areas.

Washington called on the Syrian government and all other parties in the country to immediately grant humanitarian access to all those in need.