KABUL (AFP) - Afghanistan on Thursday said it would release scores of alleged Taleban fighters from jail as there was no evidence against them, despite US objections that the men could return to the battlefield as Nato troops withdraw.

The releases will further strain US-Afghan relations as pressure mounts for the two countries to sign a long-delayed security deal allowing some American soldiers to stay in the country after 2014.

A meeting chaired by Afghan President Hamid Karzai "ordered the Bagram prisoners' dossier review board to free those prisoners who are innocent and against whom there is no evidence", a statement said.

US General Joseph Dunford, commander of Nato forces in Afghanistan, had earlier lodged an official objection over the releases, saying they were against an agreement signed when Bagram jail was handed over by the US in March.

Bagram jail was eventually passed to Afghan control after a public stand-off with Mr Karzai, who sees the jail as a symbol of Afghanistan's efforts to regain its national sovereignty.

The statement from Mr Karzai's office said that of the 88 prisoners, there was no evidence against 45 of them and only circumstantial information against 27.

The other 16 will be kept in jail and their cases reviewed.

"We can not keep Afghans in detention without any evidence - that would be illegal," presidential spokesman Aimal Faizi told AFP.

But the US says the 88 men were responsible for over 60 Nato coalition and 57 Afghan deaths.

"At least 59 of the 88 cases could be sent directly... for prosecution in an Afghan court," a US official said in a briefing ahead of Thursday's announcement.

"The remaining 29 cases have significant investigative leads necessitating immediate referral to NDS (intelligence services) for investigation." Washington and Kabul are edging closer to signing the Bilateral Security Agreement (BSA), which would see several thousand US troops remain in Afghanistan to provide training and assistance after the Nato combat mission ends in December.

Mr Faizi said the prison releases would not affect US-Afghan ties, which hit a fresh low in recent months when Mr Karzai made a surprise decision not to sign the BSA promptly despite having vowed to do so.

Signing the BSA is a precondition for the delivery of billions of dollars in Western aid for Afghanistan, which will hold an election to choose Mr Karzai's successor in April.

President Barack Obama's deputies have warned that unless Mr 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".

A similar deal with Iraq collapsed in 2011 leading to a complete US troop pull-out, and the country is now in the grip of worsening sectarian violence.