Intelligence officials are trying to establish the identity of an American militant suspect arrested in Pakistan, but doubts grew Monday that he is Al Qaeda's U.S.-born spokesman.

Pakistani officials have contradicted each other on whether the suspect is Adam Gadahn, 31, who has appeared in videos threatening the West. Two intelligence officers and a senior government official identified the detained man Sunday as Gadahn. However, a different official Monday said the suspect was an American, but not Gadahn.

"We are trying to work out who he is," said the official, who like all Pakistani intelligence agents does not allow his name to be used. "He is an American, but he is not Adam."

The suspect was arrested recently in Pakistan's largest city, Karachi, the officials said.

Pakistan is under intense U.S. pressure to arrest Al Qaeda and Taliban leaders living on its soil.

Last month, the country arrested the Afghan Taliban No. 2 commander, Mullah Abdul Ghani Baradar, in Karachi. Unnamed officials have also claimed to have detained other leaders in the movement. News of the arrests has been murky, coming primarily through Pakistani and Afghan officials speaking anonymously. None have been presented before a court or charged.

Baradar's detention and the other reported arrests have been seen as a sign that Pakistan, which has been criticized in the past as an untrustworthy ally in the fight against Al Qaeda and the Taliban, was cooperating more fully with Washington.

Asked about the arrest, Interior Minister Rehman Malik cited unspecified reports that "some foreigners have been arrested two days back" and that he had asked for more information on their identities from the intelligence agencies, which in Pakistan operate largely independently of the civilian government.

U.S. defense, intelligence and law enforcement officials on Sunday could not verify the Gadahn's reported detention.

Pakistani agents and those from the CIA work closely on some operations in Pakistan, but it was not clear if any Americans were involved in the recent operation in Karachi or the questioning of the suspect. In the past, Pakistan has quietly handed over some Al Qaeda suspects arrested on its soil to the United States.

The arrest of an American militant in Pakistan, even if it turns out not to be Gadahn, would be another example of U.S. citizens traveling abroad to join Al Qaeda and the Taliban. Security analyst say such militants, while small in number, are especially dangerous because of their ability to travel the world easier on a Western passport.

In December, Pakistan police arrested five young U.S. Muslims who they allege were trying to link up with militant groups.

Gadahn, the first American to face treason charges in more than 50 years, has appeared in more than half a dozen Al Qaeda videos, taunting the West and calling for its destruction. The video that surfaced Sunday showed him urging American Muslims to attack their own country.

He has been on the FBI's most wanted list since 2004 and there is a $1 million reward for information leading to his arrest. He was charged with treason in 2006 and faces the death penalty if convicted. He was also charged with two counts of providing material support to a designated foreign terrorist organization.