Image copyright Reuters Image caption Afghan authorities took over running Bagram jail in March last year

Afghanistan will release scores of prisoners considered by the US to be a security threat, President Hamid Karzai's office has said.

A statement said there was not enough evidence against 72 out of 88 prisoners previously held by US forces.

Washington expressed concern over the planned releases, saying it regarded the 72 as "dangerous criminals".

The two countries have been at loggerheads over Mr Karzai's refusal to sign a security deal with Washington.

'Irreparable damage'

Hundreds of prisoners at Bagram jail have been freed since the Afghan government took over the running of the prison in March 2013.

The government now says there is no evidence against 45 out of 88 further prisoners, while the evidence against 27 more is not enough to put them on trial.

"We cannot allow innocent Afghan citizens to be kept in detention for months and years without a trial for no reason at all," Mr Karzai's spokesman, Aimal Faizi, told the Reuters news agency.

Image copyright AFP Image caption US-led forces are to hand over all security duties to Afghan troops by year's end

"We know that unfortunately this has been happening at Bagram, but it is illegal and a violation of Afghan sovereignty."

US state department spokeswoman Jen Psaki said there was "strong evidence" linking the 72 to "terror-related crimes".

"We have expressed our concerns over the possible release of these detainees without their cases being referred to the Afghan criminal justice system," she said.

"These insurgents could pose threats to the safety and security of the Afghan people and the state."

US senators visiting Kabul last week said that any releases would "do irreparable damage to the relationship" between Washington and Kabul and jeopardise US plans to keep a troop presence in Afghanistan after the Nato withdrawal later this year.

A statement released by the US last week said it would constitute a breach of a memorandum of understanding agreed between the two sides at the time of the Bagram jail handover.

According to the UN Security Council's mandate, the US-led international military force in Afghanistan is scheduled to hand over all security duties to Afghan forces before its full withdrawal by the end of 2014.

But if a "Security and Defence Co-operation Agreement" is signed between the two countries, about 10,000 US troops could stay in Afghanistan for another 10 years.

The BBC's Bilal Sarwary in Kabul says that there have been internal battles within the Afghan government over the issue of prisoner releases.

He says that President Karzai's chief of staff Karim Khuram is widely perceived as being anti-American and it is an ally of his - the prison warden at Bagram jail - who is thought to be behind the decision to release the prisoners.