The top US negotiator in talks to secure a long-term security deal with Afghanistan has warned that President Hamid Karzai is unlikely to sign the agreement on time, The Washington Post reported Thursday.

The assessment was made in recent days by US Ambassador James Cunningham in a classified cable, after President Barack Obama's administration repeatedly extended the deadline for the agreement, originally due to be signed early last fall.

White House spokesman Jay Carney said this week that the deal must be signed within "weeks and not months."

"The clock is ticking," he said.

But Cunningham said he did not expect Karzai to agree to sign the document before presidential elections set to be held in April.

US-Afghan ties hit a new low in recent months after Karzai made a surprise decision not to sign the Bilateral Security Agreement promptly, despite having vowed to do so.

The BSA would see several thousand US troops remain in Afghanistan to provide training and assistance after the NATO combat mission ends in December.

Signing the BSA is a precondition for the delivery of billions of dollars in Western aid for Afghanistan.

"We continue to urge President Karzai to sign the BSA promptly," a senior State Department official told the Post when asked about Cunningham's cable.

President Barack Obama's deputies have warned that unless Karzai relents on the security deal soon, there will be no option but to prepare for a full US troop exit -- the so-called "zero option".

"If we cannot conclude a bilateral security agreement promptly, then we will be forced to initiate planning for a post-2014 future in which there would be no US, nor NATO troop presence in Afghanistan," Carney warned Monday.

"That's not the future we're seeking," he added. "But the further this slips into 2014, the more likely that outcome will come to pass."

In a separate incident that will further strain ties between Kabul and Washington, Afghanistan said Thursday that it would release scores of alleged Taliban from jail as there was no evidence against them, despite US objections that the men could return to the battlefield as NATO troops withdraw.

A meeting chartered by Karzai ordered the release.

Source: AFP