Updated at 5:33 a.m. Eastern.
An American member of al Qaeda was picked up in a raid in Pakistan's southern city of Karachi, Pakistani officials said Monday, but reversed earlier assertions that the detained man was the terror network's U.S.-born spokesman.
They identified the suspect as Abu Yahya Majadin Adam, but gave no details on his background or role within al Qaeda. CBS News' terror monitoring unit has found no previous mention in online jihadi propaganda of an individual with that name.
A name very close to that is listed on the FBI's Web site as an alias for Adam Gadahn, the 31-year-old spokesman who has appeared in several videos threatening the West since 2001. The resemblance created confusion among officials Sunday, leading them to believe that the suspect was Gadahn, an army officer and a senior intelligence officer said.
"The resemblance of the name initially caused confusion but now they have concluded he is not Gadahn," said an intelligence officer, who like all Pakistani intelligence agents does not allow his name to be used. "He feels proud to be a member of al Qaeda."
News of the arrest came as a suicide bomber in a vehicle reportedly carrying almost a ton of explosivesused to interrogate high-value terror suspects. The blast killed at least 11 people and proved the militants are still capable of carrying out major attacks in big Pakistani cities, away from the lawless border region with Afghanistan.
U.S. Embassy spokesman Rick Snelsire said the embassy had not been informed of any American being arrested.
On Sunday, two intelligence officers and a senior government official identified the detained man as Gadahn and said he was arrested in recent days. They too spoke on condition of anonymity. The government official said his name could not be used because of the sensitivity of the information. None of those officials were available for comment Monday.
"This is not looking like Gadahn," a Pakistani security official told CBS News' Farhan Bokhari late Sunday. "But it is still the arrest of an important Taliban militant."
U.S. defense, intelligence and law enforcement officials could not verify Sunday that Gadahn was the one detained.
Western diplomats in Islamabad tell Bokhari the latest arrest is significant as evidence of Pakistan's increasing success in nailing down hardcore militants, even if it proves not to be Gadahn.
"It is still not an unimportant development. But let's hold our breath before coming to a final conclusion," one diplomat in Islamabad told CBS News on condition of anonymity. "We may be groping in the dark until someone, especially the Pakistanis who are holding this man, agree to present him publicly."
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. 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 of the suspects 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 in Karachi, 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 operate largely outside of the control of the civilian government.
Pakistani agents and those from the CIA work closely on some operations in Pakistan, but it was unclear if any Americans were involved in the recent operation in Karachi or were questioning 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 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 more easily on a Western passport.
In December, Pakistani police arrested five young U.S. Muslims who they allege were trying to link up with militants.
Gadahn, the first American to face treason charges in more than 50 years, has appeared in more than a half-dozen al Qaeda videos, taunting the West and calling for its destruction. A video that surfaced Sunday showed him urging American Muslims to attack the U.S.
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.