There is another American citizen, possibly with dual citizenship, being detained for fighting on the side of the Taliban militia in Afghanistan, a senior defense official told Fox News late Wednesday.

The official said the man is being held at Camp X-Ray, the U.S. detention center in Guantanamo Bay, Cuba. The official said he has been claiming to be a citizen of the United States for weeks, perhaps months.

The Pentagon refused to officially release the man's name, but the defense source said his name was Yasser Esam Hamdi.

A Pentagon spokesman did confirm, however, that one of the 300 prisoners the U.S. military is holding in Guantanamo Bay claims he was born in Louisiana to Saudi parents and is an American citizen. Once the claim is confirmed, it could lead to his transfer from the detention center at a Navy base.

The Justice Department found a birth certificate in the state that appears to match the man's claim, Defense Department spokesman Bryan Whitman said. Whitman also declined to identify the prisoner.

The man says he was born in Baton Rouge, La., while his parents were working in the state, and he accompanied them to Saudi Arabia when he was a toddler, Whitman said.

The man was captured after a November prison uprising in the northern Afghanistan city of Mazar-e-Sharif, Whitman said. John Walker Lindh, the Californian who joined the Taliban, also was captured after that uprising, during which a CIA agent was killed.

Children born in the United States automatically are American citizens. If the detainee's claim is true, he would be a U.S. citizen unless he had renounced or otherwise changed that citizenship.

The detention center at the base in Guantanamo Bay is not meant to hold U.S. citizens, military officials have said.

The Defense Department does not believe the man's claim would affect the military's right to hold him as a battlefield prisoner, but military officials are discussing the issue with the Justice Department, Whitman said.

Walker is being held in Alexandria, Va., while he awaits trial. He is charged in federal court with conspiring to murder U.S. nationals, providing support and services to foreign terrorist organizations including Al Qaeda and using firearms and destructive devices during crimes of violence.

Three of the 10 charges carry a maximum life sentence; the other seven have prison terms of up to 90 years.

Fox News' Chris Wright and Bret Baier and The Associated Press contributed to this report.