Several American government officials gave details about the raid on the condition that they not be named, because the operation was classified.

American officials believe that besides running the Taliban’s military operations, Mullah Baradar runs the group’s leadership council, often called the Quetta Shura because its leaders for years have been thought to be hiding near Quetta, the capital of Baluchistan Province in Pakistan.

A spokesman for the Taliban insisted on Tuesday that Baradar was still free.

“This is just rumor spread by foreigners to divert attention from the Marja offensive,” said the spokesman, Zabiullah Mujahid.

“They are facing big problems in Marja. In reality there is nothing regarding Baradar’s arrest. He is safe and free and he is in Afghanistan.”

The participation of Pakistan’s spy service could suggest a new level of cooperation from Pakistan’s leaders, who have been ambivalent about American efforts to crush the Taliban. Increasingly, the Americans say, senior leaders in Pakistan, including the chief of its army, Gen. Ashfaq Parvez Kayani, have gradually come around to the view that they can no longer support the Taliban in Afghanistan  as they have quietly done for years  without endangering themselves. Indeed, American officials have speculated that Pakistani security officials could have picked up Mullah Baradar long ago.

The officials said that Pakistan was leading the interrogation of Mullah Baradar, but that Americans were also involved. The conditions of the questioning are unclear. In its first week in office, the Obama administration banned harsh interrogations like waterboarding by Americans, but the Pakistanis have long been known to subject prisoners to brutal questioning.

American intelligence officials believe that elements within Pakistan’s security services have covertly supported the Taliban with money and logistical help  largely out of a desire to retain some ally inside Afghanistan for the inevitable day when the Americans leave.