UNITED NATIONS — The leader of a Western-backed rescue organization that searches for survivors of bombings in Syria was denied entry into the United States this week, where he was to receive an award recognizing his contributions to humanitarian relief.

Raed Saleh, the head of the Syria Civil Defense, was to accept the award from InterAction, an alliance of aid agencies, at its gala dinner Tuesday night in Washington. The dinner’s keynote speaker was Gayle Smith, the administrator of the United States Agency for International Development.

But when Mr. Saleh, who works in Syria and Turkey, arrived Monday at Washington’s Dulles International Airport on a flight from Istanbul, the authorities said he could not enter the United States. He was told his visa had been canceled.

It was unclear whether Mr. Saleh’s name might have shown up on a database, fed by a variety of intelligence and security agencies and intended to guard against the prospect of terrorism suspects slipping into the country.