The French national, Naamen Meziche, was captured in a raid in the Baluchistan region near the border with Iran, officials said, without specifying when this took place. The officials did not give their names, in keeping with the policy of the Pakistani security forces.
Torsten Voss, the deputy head of Hamburg's branch of Germany's domestic intelligence service, said Meziche was known to be part of the militant scene in the northern port city. Voss said Meziche left the city for Pakistan in 2009 with a number of others.
Among those were Ahmad Wali Siddiqui, who last month was found guilty of membership in a terrorist organization and sentenced to six years in prison.
Siddiqui was captured by U.S. troops in Afghanistan in 2010. Information he provided to authorities on alleged al-Qaeda plots targeting European cities prompted Germany and other nations to raise alert levels at Christmas time that year, but no attacks materialized.
Another in the group was German-Syrian dual national Rami Makanesi, who was convicted last year in a Frankfurt state court of membership in al-Qaeda and sentenced to four years and nine months in prison. He was arrested in Pakistan in June 2010 and extradited to Germany.
The two have implicated Meziche in also training at the same al-Qaeda camps in the Pakistan-Afghanistan border region, Voss said.
In Pakistan, the officials said Meziche was a close associate of Younis al-Mauritani, whom Pakistani security forces arrested last year in a joint operation with the CIA. That arrest also took place in Baluchistan. U.S. officials said al-Mauritani was believed to have been plotting attacks in Europe.
A senior Pakistan security official said al-Mauritani's interrogation led officials to Meziche. He was arrested while trying to flee the country, likely on his way to Somalia, said the official. If Meziche is found to have broken the law in Pakistan, he would be charged and tried inside the country, the official said. Otherwise, he would be deported to France.
Baluchistan also borders Afghanistan to the northeast and has been a hotbed of militant activity.
The arrest highlights the Pakistani security forces' key role in the anti-al-Qaeda campaign, even as the United States and Pakistan are going through a rocky period.
The U.S. raid on the Pakistani city of Abbottabad that killed Osama bin Laden last year raised questions about whether Pakistani security officials at some level knew of the al-Qaeda leader's presence. The raid infuriated the Pakistani military because it was not told about it ahead of time and proved powerless to stop it.
Then in November, U.S. forces accidentally killed 24 Pakistani border troops. Pakistan closed supply lines to American and NATO forces in Afghanistan and is demanding an apology from the United States.
The United States has accused Pakistan of not doing enough to confront militant groups. During a June 7 visit to Kabul, Defense Secretary Leon Panetta said the United States was losing patience with Pakistan over its failure to go after the Haqqani network, considered one of the most dangerous groups in Afghanistan.
Pakistan says the United States does not recognize the price it has paid for taking on militant groups, a battle that has killed tens of thousands of Pakistani civilians and security forces.
Complicating the picture further is Pakistan's internal political turmoil.
The Supreme Court dismissed Gilani and his cabinet Tuesday for his failure to ask Switzerland to investigate an ally, President Asif Ali Zardari, for corruption.
On Wednesday, Pakistan's president summoned parliament to meet Friday to elect a new prime minister. In moving quickly to install a new premier, the government may reduce fears of major upheaval.