US and Pakistani spies have captured the Taliban's top military commander, media reported, dealing a huge blow to the Afghan insurgency just as American-led troops pressed an offensive against a southern stronghold.

NONE Mullah Abdul Ghani Baradar was arrested in Pakistan's sprawling port city of Karachi "several days ago" by US and Pakistani intelligence services and was under interrogation, The New York Times and other media said, citing unnamed officials in both countries.

His arrest, if confirmed, would signal a watershed in Washington's bid to persuade Pakistan to move aggressively against Islamist militants operating on both sides of the Afghan-Pakistani border.

Barader is the most important Taliban leader to be captured since the 2001 US-led offensive that ousted the Taliban from power in Afghanistan in response to the September 11 attacks on the United States.

US officials had long complained that Islamabad's spy service was failing to crack down on Afghan Taliban figures but had recently refrained from public criticism while Washington doled out billions in military and civilian aid.

Baradar's reported arrest emerged as 15,000 US, NATO and Afghan troops staged a major assault against the Taliban bastion of Marjah in southern Afghanistan, key to Washington's new strategy for turning around the troubled war.

Taliban denis mullah's capture

The Taliban, however, denied Baradar's capture and accused US officials of trying to deflect attention from the battle in Marjah.

NONE "We strongly reject the reports of his arrest," Taliban spokesman Yousuf Ahmadi told AFP by telephone from an undisclosed location.

"He is currently in Afghanistan, where he is leading all jihadi activities... The sole goal of such baseless reporting and propaganda is to make up for the failure in Marjah."

The White House refused to confirm his capture but said it welcomed better cooperation between the United States and Pakistan against "extremists."

"I think we have in the course of many months seen an increase in that cooperation," President Barack Obama's spokesman Robert Gibbs 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 Taliban and its allies have come under unprecedented pressure in recent months as Pakistan has carried out a military offensive in the country's northwest, US-led forces have pushed into the south and Washington has stepped up drone bombing raids on their safe havens in Pakistan.

'Propaganda': Islamabad

Islamabad's ties with the United States are controversial in Pakistan, where Interior Minister Rehman Malik stopped short of confirming or denying that Baradar was in custody, but criticised the report as "propaganda".

NONE The United States previously has taken out other Taliban figures, often in missile strikes by unmanned drones, but no one as senior as Baradar - who ran day-to-day operations for the insurgency.

The Afghan-born Baradar is known as a powerful military chief and trusted aide to the Taliban's one-eyed and elusive leader Mullah Mohammad Omar.

"Mullah Baradar was a close friend of Mullah Omar and both are of the same age group. He was among some 30 people considered founders of the Taliban movement," said Pakistan-based Taliban expert Rahimullah Yusufzai.

Born in the southern Afghan province of Uruzgan to the Popalzai tribe, Baradar fought in the war - covertly backed by the United States and Pakistan - to expel the Soviet forces that occupied Afghanistan in the 1980s.

NONE When the Taliban rose to power in 1996, Baradar's ties to Omar helped secure him the position of deputy defense minister, before the hardline Taliban regime was toppled by the US-led invasion in 2001 for sheltering Al-Qaeda.

Baradar is in charge of the Taliban's military operations and leadership council, and was reportedly a close associate of Al-Qaeda leader Osama bin Laden before the September 11, 2001 attacks on the United States.

The report has fed speculation about why Pakistan may have shifted its approach to the Afghan Taliban, as it had retained ties to some militants as a hedge against India's possible influence in the region.

- AFP