A senior Taliban military commander has been captured in the Pakistani city of Karachi, US officials have told Al Jazeera.
Mullah Abdul Ghani Brader is believed to be the Afghan Taliban's second-most important leader and a trusted friend of Mullah Omar, the Taliban leader.
According to officials he was seized in a secret raid by US and Pakistani intelligence forces several days ago.
He is now reportedly being interrogated by US and Pakistani agents.
However, a Taliban spokesman denied reports of Mullah Brader's capture, saying he was still in Afghanistan actively organising the group's military and political activities.
||Born in Dehrawood district of Uruzgan province, in 1968
||Number two to Taliban founder Mullah Omar
||In charge of Taliban's military operations and financial affairs
||Former defence minister for the Taliban
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"Mullah Brader has not been arrested, he is in Afghanistan, I totally refuse this rumour," Qari Mohammed Yousef, a spokesman for the Taliban, said in a statement.
"Whoever has made this propaganda, it is totally false… With this sort of propaganda they want to affect the heart of Muslims. I assure all Muslims in Afghanistan and abroad that Mullah Brader has not been arrested, he is in Afghanistan."
US media reports have described Mullah Brader's arrest as the most significant Taliban figure captured since the start of the Afghanistan war.
He is believed to have been in day-to-day command of the group's leadership council, the so-called Quetta Shura, ever since the group's founder and leader, Mullah Mohammed Omar, disappeared from view in the aftermath of September 11 attacks in 2001.
Al Jazeera's Zeina Khodr, reporting from the Afghan capital, Kabul, said Mullah Brader's capture would be a significant step.
"Mullah Brader would be a very good source, concerning information about the Taliban leadership, simply because as far as we know, he has a very good relationship with Mullah Omar, and their relationship goes back to the days when the Taliban were really in power," she said.
"Mullah Brader was a man in charge of military operations who was given the opportunity to make decisions. The ultimate decisions were made by Mullah Omar, but Mullah Brader really played an important role."
It has recently been suggested that Mullah Brader may have fallen out with the Taliban leadership.
"Mullah Brader has become a liability because sources say he was taking part in negotiations with the Afghan government between Taliban leaders, and the UN special representative to Afghanistan, Kai Eide," our correspondent said.
"His alleged involvement in secret peace negotiations in Dubai may have angered hardliners who in turn gave him up to Pakistan and American authorities."
Speaking to Al Jazeera, Hamid Gul, the former head of Pakistan's Inter-Services Intelligence (ISI), said that the fact the arrest had reportedly been made during a joint operation by US and Pakistani agents was "unusual".
"This is rather unusual, one of the top leaders of the Taliban leaders being caught here and that it was reported that this was a joint operation between the US and Pakistan intelligence this was unprecedented," he said.
|Mullah Omar, pictured, has been "in hiding" since the September 11 attacks in 2001
The US and Afghanistan have repeatedly pressed Pakistan to do more to combat Afghan Taliban and al-Qaeda fighters operating on its territory.
Arturo Munoz, a senior political scientist at the RAND Corporation who previously spent almost three decades working for the CIA, told Al Jazeera he believed Mullah Brader's arrest in a joint operation with the US was a sign of a new strategy by Pakistan.
Pakistani authorities, he said, had begun to see the Taliban as a threat to national security.
"This kind of decision to capture Mullah Brader, would not have been taken without the concurrence of the highest authorities in the Pakistani government," he said.
"The Pakistanis have now embarked on a new strategy, that they will not tolerate, to the same degree at least, this kind of insurgent activity on their borders."
The White House has not publically confirmed Mullah Brader's capture, but it did say that there had increased co-operation by Pakistani authorities in tackling the Taliban and al-Qaeda.
"I think we have in the course of many months seen an increase in that co-operation," Robert Gibbs, the White House spokesman, told reporters.
"We've seen an increase in Pakistani pushback on extremists in their own country, which I think is beneficial not simply for us."
The arrest came as US-led forces across the border in Afghanistan undertake one of Nato's biggest offensives against the Taliban.
The assault, one of the biggest in the eight-year war, is the first test of US President Barack Obama's plan to send 30,000 more troops to Afghanistan, where the Taliban has made a steady comeback since a US-led invasion ousted it from power in 2001.