The two suspects were captured this week during a raid on a house in Quetta, the capital of Pakistan's southwestern Baluchistan province, said one of the intelligence officials, who spoke on condition of anonymity because he is not authorized to speak to 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 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.
The U.S. government last year 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 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.
Al-Suri was born is Syria and also has Spanish nationality. His name has also been linked to 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 was nabbed after a shootout in a northwestern town. He was later handed over to the United States.
On Wednesday, a suspectedfrom a U.S.-run detention facility in Afghanistan poses a serious threat to Southeast Asian security, anti-terror officials said. Some said Washington failed to tell them Omar al-Farouq was free.
Al-Farouq, born in Kuwait to Iraqi parents, was considered one of Osama bin Laden's top lieutenants in Southeast Asia until Indonesian authorities captured him in 2002 and turned him over to the United States.
It was not clear how he and three other suspected Arab terrorists broke free from a heavily fortified detention facility in Bagram in July — though they reportedly claimed in a video broadcast earlier this month that they picked the lock of their cell.
Several razor-wire fences surround the base and areas outside the perimeter remain mined from Afghanistan's civil war and Soviet occupation. Military teams patrol constantly and the main entrance is a series of heavily guarded checkpoints.
Though the escape was widely reported at the time, al-Farouq was identified by another name.