(CNN) — Adam Gadahn, an American spokesman for al Qaeda, has been arrested in Pakistan, a senior Pakistani government official source told CNN.

The official said Gadahn was arrested Sunday in Karachi.

Several U.S. officials told CNN that they have no indication that Gadahn has been captured.

News of the arrest came hours after Islamist Web sites posted video of Gadahn praising a November shooting rampage at the U.S. Army base in Fort Hood, Texas. On the video, Gadahn said the Army major charged with gunning down 13 people “lit a path” for other Muslim service members to follow.

Gadahn has routinely posted lengthy videos on Islamist online forums.

In 2006, he was indicted on charges of treason and providing material support to terrorists. The U.S. government has offered a US$1 million reward for information leading to his capture.

Gadahn grew up on a California farm, and was home-schooled until age 17. A year later he moved in with his paternal grandparents, who were secular Jews. He converted to Islam at the Islamic Society of Orange County, California, but was banned from the mosque two years later after hitting its chairman, Haitham Bundjaki.

In 1997 Gadahn began working for a California charity suspected of having ties to al Qaeda. He moved to Pakistan in 1998.

His family has said they last heard from him in 2002. In 2004, the FBI identified him as part of an al Qaeda cell that was planning attacks aimed at disrupting that year’s presidential election in the United States.

In October 2004, he began appearing in disguise in al Qaeda videos. Gadahn dropped the disguise in 2006.

In 2008, he renounced his U.S. citizenship and destroyed his passport in another al Qaeda video.

In his video message posted online Sunday, Gadahn says Muslims should emulate the alleged Fort Hood shooter.