President Ashraf Ghani's comments pointed to the first hitch in implementing the fragile deal, which is aimed at ending America's longest war after more than 18 years and getting rival Afghan factions to agree on their country's future.

Still, the U.S. has said a planned U.S. troop withdrawal over the next 14 months is linked to the Taliban's counter-terrorism performance, not to progress in intra-Afghan talks.

The U.S.-Taliban deal signed Saturday envisions the release of up to 5,000 Taliban prisoners by the Afghan government ahead of talks between Afghan factions meant to begin March 10 in the Norwegian capital of Oslo. The Taliban would release up to 1,000 prisoners.

Ghani told a news conference in the Afghan capital of Kabul on Sunday that this wasn't a promise the United States could make. He said the release of prisoners was a decision for his government to take and that he wasn't ready to release prisoners before the start of negotiations.

"The request has been made by the United States for the release of prisoners and it can be part of the negotiations but it cannot be a precondition," Ghani said.

The U.S.-Taliban deal is seen as a historic opportunity to extricate the United States from Afghanistan, a nation convulsed by conflict since the Soviet invasion in December 1979. Yet it could also unravel quickly, particularly if the Taliban fail to deliver on a promise that no terror attacks would be launched from Afghan soil.

The intra-Afghan talks between squabbling political factions and rival Taliban in Afghanistan are even more intricate — even if a potential failure might not slow the withdrawal of American forces.

In an interview with The Associated Press, Qatari Foreign Minister Mohammad bin Abdulrahman Al Thani said he considered a prisoner exchange an important confidence-building measure.

 "What we have here is a 14-months agreement that, including in these 14 months, there are several things that need to be accomplished because everything is interconnected," he said Sunday.

"And in that agreement, the prisoner exchange will be one of the first confidence-building measures, so it will remain a very critical step that we need to push forward. And we have the delegations ready for the meeting (with) Taliban and others. So I hope that the negotiations will start very soon."