KARACHI: The American-born spokesman for al-Qaida has been arrested by Pakistani intelligence officers in the southern city of Karachi, two officers and a government official said on Sunday, the same day Adam Gadahn appeared in a video urging US Muslims to attack their own country.

The arrest of Gadahn is a major victory in the US-led battle against al-Qaida and will be taken as a sign that Pakistan is cooperating more fully with Washington. It follows the recent detentions of several Afghan Taliban commanders in Karachi.

Gadahn — who has often appeared in al-Qaida videos — was arrested in the sprawling southern metropolis in recent days, two officers who took part in the operation said. A senior government official also confirmed the arrest.

They spoke on condition of anonymity because they were not authorized to release the information.

Gadahn grew up on a goat farm in Riverside County, California, and converted to Islam at a mosque in nearby Orange County.

He moved to Pakistan in 1998, according to the FBI, and is said to have attended an al-Qaida training camp six years later, serving as a translator and consultant for the group. He has been wanted by the FBI since 2004, and there is a $1 million reward for information leading to his arrest or conviction.

The 31-year-old is known by various aliases including Yahya Majadin Adams and Azzam al-Amriki.

He has posted videos and messages calling for the destruction of the West and for strikes against targets in the United States. The most recent was posted Sunday, praising the US Army major charged with killing 13 people in Fort Hood, Texas, as a role model for other Muslims.

A US court charged Gadahn with treason in 2006, making him the first American to face such a charge in more than 50 years. He could face the death penalty if convicted. He was also charged with two counts of providing material support to a designated foreign terrorist organization.

Gadahn has appeared in more than half a dozen al-Qaida videos. The video released Sunday appeared to have been made after the end of the year, but it was unclear exactly when.

Dawud Walid, the executive director of the Michigan chapter of the Council on American-Islamic Relations in Southfield, Mich., condemned Gadahn’s call for violence, calling it a “desperate” attempt by Al-Qaida’s spokesman to provoke bloodshed within the US

Walid, a Navy veteran, said Muslims have honorably served in the American military will be unimpressed by al-Qaida’s message aimed at their ranks.

“We thoroughly repudiate and condemn his statement and what we believe are his failed attempts to incite loyal American Muslims in the miltary,” he said.

Imad Hamad, the senior national adviser for the American-Arab Anti-Discrimination Committee, based in Dearbon, Mich., condemned al-Qaida’s message and said it would have no impact on American Muslims.

“This a worthless rhetoric that is not going to have any effect on people’s and minds and hearts,” he said.

Al-Qaida has used Gadahn as its chief English-speaking spokesman, and he has called for the destruction of the West and for strikes against targets in the United States. In one video, he ceremoniously tore up his American passport. In another, he admitted his grandfather was Jewish, ridiculing him for his beliefs and calling for Palestinians to continue fighting Israel.