Raed Saleh, a Syrian national, landed at Dulles International Airport outside Washington on Monday afternoon after an 11-hour journey from Turkey. In his passport was a visa for the U.S.

He was planning to attend a Tuesday evening banquet in the capital where he was being honored for his rescue work in Syria. But as Saleh tried to make his way through immigration, he says, he was pulled aside by security at the airport.

"After about two or three hours, they told me, 'We apologize but you must return to Turkey because this visa has been canceled. It's not valid.' I told them, 'How isn't it valid? It's good for six months.' "

Saleh says the immigration official could not tell him why he was being turned back.

"He told me, 'I don't have any explanation or details. I can't tell you anything,' " according to Saleh, who spoke to NPR via Skype. He was in Geneva, on his way back to Turkey.

Saleh had to head back without the award he was to receive from InterAction, an alliance of international humanitarian and aid agencies.

Saleh heads up Syria Civil Defense, also known as the White Helmets, a collection of 2,800 volunteer rescue workers who help victims caught up in the war.

"Their group really responds when buildings have been damaged from bombings or other kind of strikes and they go in and they pull people out of the rubble," says Nancy Wilson, the head of Relief International, which nominated Saleh for the award.

Wilson says the awards dinner carried on without Saleh — but many in the audience honored him by wearing white helmets, the trademark of his group.

Wilson says she's surprised Saleh wasn't allowed into the U.S.

"He has been to the United States before, spoken at the U.N. Security Council, was allowed on the plane — which is not an easy thing in Turkey to begin with because they scrutinize your visa papers there," she says. "And then for him to get here, and then not be able to actually be allowed in the country is just very disappointing."

The still-unanswered question is why Saleh was turned back.

The Department of Homeland Security issued a statement saying a number of U.S. agencies have a say in determining whether someone can enter the country. They include the State Department and law enforcement agencies.

The keynote speaker at the dinner was Gayle Smith, who heads the U.S. government's Agency for International Development. But she didn't shed any light on the matter.

For his part, Saleh says he felt demoralized by the incident, but knows it's not unusual for Syrians traveling abroad.

"Honestly, this is a problem across the board," he says. "For the Syrians in any airport in the world. It's become common."

One of Saleh's colleagues will deliver the award to him in Istanbul.

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