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 Sunday as video emerged of him urging US Muslims to attack their own country.

This image from video released by IntelCenter Sunday, March 7, 2010, shows Adam Gadahn, featured in a video posted Sunday, coincidentally the day that his arrest by Pakistani intelligence officers in the southern city of Karachi was announced.[Xinhua/AFP Photo]

The arrest of Adam Gadahn is a major victory in the US-led battle against al-Qaida and will be taken as a sign that Pakistan, criticized in the past for being an untrustworthy ally, is cooperating more fully with Washington. It follows the recent detentions of several Afghan Taliban commanders in Karachi, including the movement's No. 2 commander.

US officials did not immediately confirm Gadahn's capture.

Gadahn has appeared in more than half a dozen al-Qaida videos, taunting and threatening the West and calling for its destruction. 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 was arrested in the sprawling southern metropolis of Karachi in recent days, two officers who took part in the operation said. A senior government official also confirmed the arrest, but said it happened Sunday. The discrepancy could not immediately be resolved.

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

The intelligence officials said Gadahn was being interrogated by Pakistani officials. 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 operation or questioning.

In the past, Pakistan has handed over some al-Qaida suspects arrested on its soil to the United States.

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. 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 treason charge carries the death penalty if he is convicted. He was also charged with two counts of providing material support to a designated foreign terrorist organization.

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

His most recent video was posted Sunday, praising the US Army major charged with killing 13 people in Fort Hood, Texas, as a role model for other Muslims. The video released Sunday appeared to have been made after the end of the year, but it was unclear exactly when.

"You shouldn't make the mistake of thinking that military bases are the only high-value targets in America and the West. On the contrary, there are countless other strategic places, institutions and installations which, by striking, the Muslim can do major damage," Gadahn said, an assault rifle leaning up against a wall next to him.

Pakistan joined the US fight against Islamist extremists following the September 11, 2001, attacks, and several high-ranking al-Qaida and Taliban have been arrested. But critics have accused the country of not fully cracking down on militants, especially those who do not stage attacks in Pakistan, all the time while receiving billions of dollars in US aid.

Osama bin Laden is believed to be hiding somewhere in the country, most likely close to the Afghan border.

Al-Qaida has used Gadahn as its chief English-speaking spokesman. 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.

Dawud Walid, the executive director of the Michigan chapter of the Council on American-Islamic Relations in Southfield, Michigan, 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 and 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 military," he said.

Imad Hamad, the senior national adviser for the American-Arab Anti-Discrimination Committee, based in Dearborn, Michigan, 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.

The last person in the US convicted of treason was Tomoya Kawakita, a Japanese-American sentenced to death in 1952 for tormenting American prisoners of war during World War II. President Eisenhower later commuted his sentence to life imprisonment.

Gadahn was last known to be in Southern California in 1997 or 1998. His mother last spoke to him by phone in March 2001. At the time he was in Pakistan, working at a newspaper, and his wife was expecting a child.

Appearing in 2006, in a 48-minute video along with al-Qaida's No. 2 leader, Ayman al-Zawahri, Gadahn called on his countrymen to convert to Islam and for US soldiers to switch sides in the Iraq and Afghan wars.