Mullah Abdul Ghani Brader, a senior Taliban military commander, has been captured in Karachi, Pakistan's largest city, a US newspaper has reported.
According to The New York Times, Mullah Brader, the Taliban's number two, was captured in a secret raid by US and Pakistani intelligence forces several days ago.
Citing US government officials, the paper said Mullah Brader had been in Pakistani custody for several days and was being interrogated by US and Pakistani intelligence.
The paper described him as the most significant Taliban figure captured since the start of the Afghanistan war.
But a Taliban spokesman denied the report of his capture, saying he was still in Afghanistan actively organising the group's military and political activities.
"He has not been captured. They want to spread this rumour just to divert the attention of people from their defeats in Marjah and confuse the public," Zabihullah Mujahid told Reuters, referring to a US-led Nato offensive in Afghanistan's Helmand province.
Mullah Brader has been in day-to-day command of the group's leadership council, the 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 capital Kabul, said Mullah Brader's capture, if true, is "significant".
"But 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."
Our correspondent, however, indicated that Mullah Brader may have had a fallout with the 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. Of course the Taliban deny that any such meetings took place.
Speaking to Al Jazeera, Hamid Gul, the former head of Pakistan's Inter-Services Intelligence (ISI), said Mullah Brader's capture may not deal a body blow to the Taliban.
"The Taliban is not a monolithic organisation ... I don't think his capture is going to affect the ability of the Taliban to resist the onslaught that the Americans want to launch," he said.
'Joint raid'
The New York Times report said it was not clear if he was talking, but quoted the officials as saying his capture could lead to other senior Taliban leaders.
The officials voiced hope Mullah Brader would provide the location of Taliban leader Mullah Muhammad Omar.
The New York Times cited officials as saying the operation to capture Mullah Brader was conducted by ISItogether with CIA operatives.
The newspaper said it learned of the operation on Thursday, but delayed reporting it after a request by White House officials who said disclosing it would end a very successful intelligence drive.
The New York Times said it was now publishing the report because White House officials acknowledged that news of the capture was becoming broadly known in the region.
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 in 2001.
