Pakistani security agencies have arrested two Al Qaeda suspects and are investigating whether one is a Syrian believed to be a key figure in Usama bin Laden's terror network in Europe, two intelligence officials and a senior government official said Thursday.

The two suspects were captured this week during a raid on a house in Quetta (search), the capital of Pakistan's southwestern Baluchistan (search) province, said one of the intelligence officials, who spoke on condition of anonymity because he is not authorized to address the media.

A senior government official confirmed the arrests and said authorities were investigating whether one of the suspects was Mustafa Setmarian Nasar, alleged to have had a key role in the March 11, 2004, Madrid bombings that left 191 people dead and more than 1,500 people injured. That official also declined to be named, saying he was not allowed to comment publicly on the investigation.

Neither the intelligence officials nor the government official had information about the identity of the second suspect.

Pakistani government spokesmen and the U.S. Embassy said they could not immediately confirm the arrests.

Last year, the U.S. government announced a $5 million reward for information leading to the capture of Nasar, also known as Abu Musab al-Suri.

The U.S. Justice Department's Rewards for Justice (search) Web site describes Nasar as an Al Qaeda member and former trainer at terrorist camps in Afghanistan who instructed extremists in using poisons and chemicals. It also says he is likely to be in Afghanistan or Pakistan.

Nasar, 47, was born in Syria and also has Spanish nationality. His name has also been linked to the July 7 bombings in London that left 52 people dead.

In September 2003, he was among 35 people named in an indictment handed down by a Spanish magistrate for terrorist activities connected to Al Qaeda, and was alleged to have close ties with the alleged leader of the terror group's cell in Spain, a Syrian-born Spaniard named Imad Yarkas.

Pakistan, a key U.S. ally in its war on terrorism, says it has arrested more than 700 Al Qaeda suspects since the Sept. 11, 2001, attacks on America, and has handed most of the suspects to the United States.

The last reported arrest of a key Al Qaeda figure in Pakistan was in May, when Abu Farraj al-Libbi, the alleged mastermind of assassination attempts against Pakistan's President Gen. Pervez Musharraf (search) was nabbed after a shootout in a northwestern town. He was later handed over to the United States.