(CNN) -- An al Qaeda member wanted for training terrorists and known for his inflammatory writings has been captured in a raid in Pakistan, two U.S. counterterrorism officials told CNN on Friday.The officials, who spoke on condition of anonymity, offered few details about the arrest of Mustafa Setmarian Nasar, who had a $5 million reward offered in 2004 for his capture.The raid took place in Quetta, a Pakistani provincial capital near the southern Afghan border.Pakistani Information Minister Sheikh Rashid Ahmad said Thursday that an al Qaeda member was captured and another was killed during a shootout in Quetta earlier this week. Ahmad did not then identify the person captured, and he was not available for comment Friday.The U.S. counterterrorism officials confirmed the man in custody was Nasar, a 47-year-old Syrian who also has Spanish citizenship. The reward poster on the Web site of the non-governmental, non-profit group Rewards for Justice said he was an al Qaeda member who had trained terrorists at two Afghan camps in the use of poisons and chemicals.One of the counterterrorism officials cautioned against overstating his importance in the terror network, saying Nasar was a "background" guy with a "number of contacts.""Nasar is best known for his writings," the official said.But the official added, "We're better off that he's captured."Spanish connectionsNasar is wanted on a 2003 Spanish arrest warrant for allegedly helping to organize in the mid-1990s one of the first al Qaeda cells in that country.He has been linked to multiple al Qaeda suspects in Madrid, including three who were charged with helping to plan the September 11, 2001, attacks in the United States, Spanish authorities said.Nasar has not been charged in the 2004 Madrid bombings that killed 191 people and wounded more than 1,500, but the prosecutor has said information about Nasar should be allowed in any trial of bombing suspects.A total of 109 people have been charged in that case. Indictments are expected later this year and a trial would follow next year. Authorities have said Nasar fled Syria in the 1980s, traveling throughout the Mideast and North Africa before settling in Madrid in 1987, where he married. He moved to London in 1995, where he penned inflammatory essays against the United States for an Islamic extremist magazine, Al Ansar. According to CNN terrorism analyst Peter Bergen, Nasar has known Osama bin Laden for a long time but had a falling out with him a number of years ago. Nasar wrote a book, "The International Islamic Resistance Call," that was published on jihadist Web sites. He discussed training at al Qaeda terrorist camps from 1988 until 1991 and later setting up his own terrorist training camps in Afghanistan just prior to the September 11 terrorist attacks.CNN's Pam Benson, Kevin Bohn, David Ensor, Al Goodman and Syed Mohsin Naqvi contributed to this report.