The official's account was the most detailed yet of the U.S. and NATO role in the clandestine talks, aimed at bringing an end to the 9-year-old war. The official spoke on condition of anonymity because he was not authorized to describe the subject publicly.

The Afghan government has previously acknowledged that it has been involved in reconciliation talks with the Taliban with some NATO help. But discussions between the two sides have been described as mostly informal and indirect message exchanges relying on mediators.

The Afghan Taliban denied the claim in a statement on its website on Wednesday. The group said the notion of talks with the enemy was "baseless propaganda" and that negotiations would be a "waste of time."

If the talks succeed, the Obama administration will have to decide whether to accept a deal struck between a government backed and funded by Washington and an enemy force with ties to al-Qaida.

The U.S and the NATO alliance are not mediating the talks, only helping to facilitate them, U.S. officials have said.

That position is unlikely to change, considering that some 140,000 NATO troops continue to fight the homegrown Islamist insurgency seeking to displace Karzai's secular government.

U.S. officials have said they hope the talks will become a "game changer" in the war. But there are many complicating factors, including what might be expected of the U.S.