LAHORE, Pakistan -- A suicide car bombing at a building that houses terrorism investigations in Lahore killed at least 13 people and wounded 80 others Monday, the first terrorist strike to hit a major city in the country's heartland this year.

The blast targeted a special investigative unit that interrogates key terrorism suspects. The entire building collapsed from the force of the blast, and rescuers spent the morning searching for survivors.

Lahore's administrative chief, Khusro Pervez, said the bomber had crashed through a security gate before ramming a perimeter wall and detonating what police said were more than 1,100 pounds of explosives.

Rana Sanaullah, law minister for Punjab province, which includes Lahore, called the attack "a sad and condemnable incident," adding: "These terrorists are trying to destabilize the country. The government will not let them succeed with their agenda."

Meanwhile, the American al-Qaida operative arrested in Karachi over the weekend turned out not to be the Southern California native wanted by the United States on treason charges for his involvement in the terror network, Pakistani intelligence officials said Monday. They suggested that he may instead be a Pennsylvania native.

Until Monday, Pakistan had been experiencing a relative lull in violence, particularly in major cities like Lahore that were hard-hit by suicide bombings last year. A wave of bombings and ambushes in 2009 that killed more than 600 coincided with large-scale military offensives by Pakistani troops against Taliban militants in South Waziristan and other tribal districts along the Afghan border.

Pakistani security forces have regained control over several Taliban strongholds in the tribal areas, but militants maintain cells throughout Pakistan and retain the capacity to unleash assaults on cities and towns.

No organization claimed responsibility for the Lahore blast. Monday's bombing was the first such attack to strike Lahore since December, when two near-simultaneous bombs tore through a crowded city market, killing at least 48 people.

Lahore Police Chief Pervez Rathore said as many as 40 counter-terrorism officials were inside the building when the blast occurred. The explosion carved out a crater about 12 feet deep and 15 feet wide. As many as 15 other buildings were partly damaged.

Pakistani security officials initially asserted that the American Islamic extremist they had captured late Saturday night in Karachi, the country's largest city, was Adam Gadahn of Riverside, Calif., a spokesman and top propagandist for al-Qaida.

But U.S. officials said they were skeptical of those claims, and that there was no indication that Mr. Gadahn was arrested.

Later Monday, Pakistani intelligence officials reversed themselves and said the man arrested was actually Abu Yahya Mujahideen Adam, a Pennsylvania native and al-Qaida operative. The intelligence officials said Mr. Adam had been transferred to Islamabad for interrogation, but would not elaborate.

Mr. Gadahn, 31, remains at large. He is on the FBI list of most-wanted terrorists and is the first American since the World War II-era to be charged with treason. The U.S. government has offered a $1 million reward for information leading to his arrest.

He was indicted in 2006 by a federal grand jury in Orange County, Calif., for allegedly providing material support to al-Qaida by appearing in videos on five occasions from Oct. 27, 2004, to Sept. 11, 2006, with the intent "to betray the United States."

His latest video, posted Sunday on extremist Web sites, urged Muslims serving in the U.S. military to emulate U.S. Maj. Nidal Malik Hasan, an Army psychiatrist accused of killing 13 people Nov. 5 at the Fort Hood military base just outside Killeen, Texas. He called Maj. Hasan "the ideal role model for every repentant Muslim in the armies of the unbelievers and apostate regimes."

Looking for more from the Post-Gazette? Join PG+, our members-only web site. You'll get exclusive sports content, opinion, financial information, discounts from retailers and restaurants, and more. Our introduction to PG+ gives you all the details.