The second-in-command of the Afghan Taliban was captured in Pakistan last week during a raid secretly carried out by Pakistani and U.S. intelligence operatives, officials from the two countries said Monday.

The arrest of Mullah Abdul Ghani Baradar deals a serious blow to the Taliban, and also represents a potential turning point for the government of Pakistan, which often has seemed reluctant to pursue top members of the militant group that previously ruled Afghanistan who now take refuge across the border.

The loss of Baradar would deprive the Afghanistan insurgency of its top-ranked military mastermind at a time when U.S. forces are in the midst of a major push to roll back Taliban gains in Afghanistan.

"It is going to be a big deal, certainly a major blow," said a senior Pakistani military official, speaking of the capture on condition of anonymity. Baradar's capture also could represent an intelligence coup for the United States, particularly if he has agreed to provide information on the whereabouts of other Taliban figures, including Mullah Mohammed Omar, the group's supreme commander, believed to be hiding in Pakistan.

Baradar was arrested in the port city of Karachi as part of a secret operation conducted by members of Pakistan's powerful Inter-Services Intelligence agency, working in conjunction with the CIA.

Baradar is in Pakistani custody, but many details about the operation remained unclear late Monday, including precisely when he was captured and whether he is cooperating.

CIA and White House officials declined to comment on the matter. Senior U.S. intelligence officials including CIA Director Leon E. Panetta have testified in recent weeks that the agency is taking part in overseas interrogations of terrorism suspects. But their comments appear to have preceded the capture of Baradar, who was a close associate of Al Qaeda leader Osama Bin Laden before the Taliban and Al Qaeda fled Afghanistan to take refuge in Pakistan after the U.S. invasion in 2001.

Baradar is the highest-ranking Taliban militant to be captured since the fighting began. He is perhaps the closest aide to Mullah Omar, and their association dates back to the movement's earliest days.

But even while professing fealty to Omar, and consistently invoking Omar's authority when dealing with others in the movement, Baradar is believed by intelligence officials to have a much greater hands-on role than his chief in masterminding military operations and disbursing Taliban money.

With the reclusive-minded Omar having retreated into something as a figurehead role, Baradar had been the principal power in the so-called Quetta Shura, the main Taliban decision-making body named for the southern Pakistani city in which it is based. Baradar has a reputation for ruthlessness, but is also described as a charismatic figure who maintains a good rapport with Taliban field commanders across Afghanistan.

He is also far better versed in technology and world affairs than the unschooled Omar, who in many respects is considered little changed from his days a village cleric.

Baradar has been an active advocate of many of the insurgent tactics that have made the past year the deadliest yet for U.S. and coalition forces in Afghanistan, said a Western military official in Afghanistan, also speaking on condition of anonymity. Those tactics include expanded use of improvised explosive devices, singling out of vulnerable U.S. bases and patrols for ambushes and raids, eschewing efforts to hold territory in favor of mobility and quickness, and studiously avoiding head-on confrontations with better armed-Western forces, melting away and regrouping later instead.

The Pakistani military official said that Barader's capture could bolster the U.S. aim of weakening the Afghan Taliban to sap its support and convince less committed elements of abandoning the fight.

"Everything you are doing is to start negotiation from a position of strength, and you are gradually getting that strength," the official said. Pakistani and Saudi Arabian intelligence officials have had secret talks with Taliban leaders in recent months to that end.

Baradar's arrest was first reported Monday night by the New York Times, which said that its reporters initially learned of the capture on Thursday, but delayed reporting it because White House officials said that doing so could jeopardize intelligence-gathering. The paper went ahead and disclosed the details because the arrest was becoming more widely known in the region.

The capture signals a potentially major change of course for the Pakistani government.

U.S. officials have repeatedly accused Islamabad of secretly providing support to the Afghan Taliban in an effort to maintain ties to the group in case it is able to reclaim power next door.

Pakistan has proven far more willing to pursue members of the Pakistani Taliban, which has carried out a series of bloody attacks inside that country aimed at destabilizing Islamabad and imposing strict Islamic law in parts of Pakistan's territory.

The capture of Baradar is likely to raise expectations that Islamabad may be prepared to move more aggressively against Mullah Omar and other top members of the Afghan Taliban movement, which is believed to be based primarily in Quetta.

The Pakistani military official downplayed suggestions that Barader's efforts signified a new direction for the government in Islamabad. "I wouldn't say it is a turning point," the official said, arguing that Pakistan has always been committed to rooting out militants, and that it has become more convinced recently of U.S. commitment to the region.

The CIA and the ISI cooperated on a series of high-level capture operations in the past, most notably in the years after the Sept. 11 attacks when the two services teamed up to snatch top Al Qaeda operatives including the alleged Sept. 11 mastermind, Khalid Sheikh Mohammed.

Those raids almost always took place in major Pakistani cities, far from the more rugged and lawless tribal regions along the Afghan border where Bin Laden and others are believed to have taken refuge. But there have been few significant captures in recent years, and the United States has instead relied on an intense campaign of missile strikes from Predator drones against Taliban and Al Qaeda targets.

Staff writer Laura King in Kabul, Afghanistan contributed to this report.