The capture of Mullah Obaidullah Akhund marked the first Pakistan arrest of a senior leader of the Islamist militia since it was driven from power in Afghanistan in 2001 when thousands of its fighters fled into Pakistan.
The security official and Taliban sources yesterday said Akhund, the third most senior member of the Taliban's 10-member leadership council, was arrested late on Monday, hours after a surprise visit to Pakistan by US Vice-President Dick Cheney.
Government and military spokesmen denied the arrest had been made when asked by sources.
The story, however, was the front page story in the Dawn, a leading Pakistani daily.
''Mullah Omar's deputy Obaidullah captured'' was the headline in a report that was also sourced to an unnamed official.
Aside from being on the leadership council headed by Mullah Mohammad Omar, Akhund was also defence minister in the Taliban government before it fell.
The arrest comes at a time when the Bush administration is facing a welter of scepticism from Democrats, the American media and several think-tanks over Pakistan's role as an ally in the war on terrorism.
Cheney had asked Pakistani President Pervez Musharraf to do more to stop al Qaeda rebuilding from safe havens in Pakistani tribal lands and step up efforts to thwart a spring offensive by the Taliban against Afghan and NATO troops.
The Pakistani security official said Akhund's arrest was the culmination of a planned operation and not a result of Cheney's visit.
Taliban sources, speaking on satellite telephones from undisclosed locations, said Akhund was caught at the home of one of his relatives at the Baluchistan provincial capital.
They said two other Taliban leaders had been arrested in Quetta this week, but the Pakistani security official could not confirm this.
While Akhund's capture would represent a major coup, it sits uneasily with Pakistan's past denials of allegations that Taliban leaders were running the Afghan insurgency from Quetta.
President Musharraf said last month that he was ''500 per cent'' sure that Mullah Omar was in Afghanistan, though he admits there are Taliban fighters in Pakistan.
The lack of arrests in the past fed speculation that Pakistani intelligence services or rogue agents have allowed Taliban leaders to operate freely.
Having supported the Taliban prior to al Qaeda's September 11, 2001, attacks on the United States, Pakistan has struggled to shake off suspicions that its spies continue to play a double game in case the West's commitment to Afghanistan does not last.
US generals have spoken of Taliban ''command and control'' centres on Pakistani territory.
Yet NATO officials have thanked Pakistan for its help in several recent counter-insurgency operations, including a US air strike that killed a senior commander, Mullah Akhtar Mohammad Osmani, in southern Afghanistan on December 19.