Gadahn, the first American to face treason charges in e than 50 years, has appeared in more than half a dozen al-Qaida videos, taunting the West and calling for its destruction.

Two Pakistani officers and a government official said Sunday that an American charged with treason for working with al-Qaida had been captured, a development that could deliver another significant blow in the U.S.-led battle against the terror network.

U.S. defense, intelligence and law enforcement officials could not immediately verify the reported detention of Adam Gadahn, a 31-year-old spokesman for al-Qaida who has appeared on videos threatening the West, including one that emerged earlier Sunday.

The reported arrest of Gadahn follows the recent detention of several Afghan Taliban commanders in Karachi, including the group’s No. 2. Those detentions have been seen as a sign that Pakistan, which has been criticized as an untrustworthy ally, was cooperating more fully with Washington.

Some observers were cautious about giving credence to the claim that Gadahn was in custody as reports emerged that the man arrested might instead be a Taliban militant leader. There was no way of independently verifying the arrest or identity, and detentions of terror suspects in Pakistan are often surrounded by conflicting reports.

“If this is him, it’s a big capture and a morale-booster,” said Patrick Rowan, the former top anti-terrorism official in the Bush Justice Department.

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