Key al-Qaida figure reportedly captured

A key figure in al-Qaida�s terror network in Europe is under arrest, U.S. counterterrorism officials tell NBC News.

Two U.S. officials, speaking on condition of anonymity, say that the alleged terrorist, Mustafa Setmariam Nasar, also known as Abu Musab al-Suri, was recently arrested in Pakistan. Pakistani government officials say they are not aware of any such arrest.

Nasar is an expert in explosives and chemicals who trained recruits at al-Qaida terror camps in Afghanistan before the Sept. 11, 2001, terrorist attacks in the United States, according to counterterror officials and Nasar's wanted poster on the State Department's Rewards for Justice Web site.

Nasar was born in Syria but is married to a Spanish woman and has Spanish nationality. He has traveled extensively in Europe and has militant connections in Europe, Pakistan and elsewhere, and security experts believe his arrest could prove to be an intelligence bonanza for the CIA and other U.S. and European counterterrorism agencies.

Nasar is known inside the US intelligence world as the �pen jihadist�, a prolific writer whose communiques carry great weight in the militant underworld. He has written extensively on the Internet of his desire to use chemical or biological weapons against the United States, an effort he has described as �dirty bombs for a dirty nation."

Last year, the U.S. government announced a $5 million reward for information leading to the capture of Nasar.