* Afghan authorities say no evidence against released prisoners
* U.S. says freed detainees linked to attacks, could pose new threat
* NATO suggests release was politically motivated (Adds presidential spokesman, new U.S., NATO statements)
By Hamid Shalizi and Abdul Saboor
KABUL, Feb 13 (Reuters) - The Afghan government released 65 detainees on Thursday despite repeated U.S. warnings that the "dangerous individuals" could return to the battlefield, further straining tense U.S.-Afghan ties as the international mission in Afghanistan winds down.
Afghan officials described the move as justice for its own citizens who faced unfounded accusations from the U.S. military. But NATO, which oversees the 12-year-old foreign military operation bolstering the Kabul government, denounced it as "a major step backward" for rule of law in the country.
Afghan Defence Ministry spokesman Zahir Azimi said the prisoners had been released from a detention facility near the Afghan capital, Kabul, and would be sent back to their respective home areas throughout Afghanistan.
Aimal Faizi, spokesman for President Hamid Karzai, said that the release marked the implementation of a decision made by Afghan judicial authorities last month.
"Innocent Afghans, who were detained illegally by the United States in Bagram prison for years, have been released. We welcome this," Faizi told Reuters.
Video provided to Reuters by the Afghan Defence Ministry showed the prisoners, with jackets or blankets over their traditional Afghan garb, shaking hands with Afghan military officials as they left the prison.
In an unusually sharp statement, the U.S. military force said some of the released detainees had killed both Afghans and foreign soldiers and now posed a fresh threat.
"The release of these dangerous individuals poses a threat to U.S., Coalition and Afghan National Security Forces, as well as the Afghan population," it said.
"U.S. and Afghan forces risked their lives to ensure the safety of the Afghan people. We call upon the (Afghan government) to consider the potentially lethal effects of today's releases."
Released without due process, the statement said, detainees "may return to the same criminal behavior that led to their original capture".
NATO Secretary General Anders Fogh Rasmussen, in a statement issued in Brussels, said he was gravely concerned.
"This decision, which appears to have been made based on political calculations and without regard for due process before the Afghan courts, is a major step backwards for the rule of law in Afghanistan, and poses serious security concerns," he said.
Karzai's government has long complained that foreign forces have locked up Afghans on dubious grounds, with no proper judicial process. Karzai is due to step down after this year's elections after more than 10 years in power.
Abdul Shakor Dadras, head of the Afghan board charged with reviewing the prisoners' cases, said their detention had been unjustified from the outset, despite information put forward against the detainees by the United States.
"We could not find any evidence to prove that these 65 people are criminals, according to Afghan law," Dadras told Reuters Television.
"I believe the release of these 65 people will benefit the Afghan nation, and it will benefit the American nation and American government."
PRISONERS WERE TRANSFERRED TO AFGHAN AUTHORITY
The prisoners were part of a much larger group of detainees transferred to Afghan authority last year as one milestone in the U.S. and NATO transition out of Afghanistan. A coalition of foreign forces has been battling the Taliban since the Islamist group was ousted in 2001.
More than 500 of those prisoners have already been released, a U.S. military official said on condition of anonymity, while others were recommended for prosecution in Afghan courts.
The 65 freed on Thursday were part of a group of 88 whose proposed release had prompted U.S. objections. The fate of the remaining 23 prisoners in the group is being examined by the Afghan government, the official said.
While U.S. officials have said that U.S. forces would try to kill or capture the men if they took up arms against them, it remains unclear if U.S. or coalition forces would try to apprehend or target them pre-emptively.
The detainees have become one more issue fuelling tension in U.S.-Afghan ties ahead of April presidential polls and the planned pullout of most foreign troops by the end of the year.
The Obama administration has been pressing Karzai for months to sign a bilateral security agreement with Washington that would allow some U.S. troops to stay beyond that deadline.
The U.S. embassy called the release a "deeply regrettable" move that violated to a 2012 deal on detainees and said the Kabul government "bears responsibility" for the decision.
The U.S. military official said the United States had provided Afghan officials with "hundreds of pages" of what he described as evidence or leads against the prisoners.
Some of the detainees, he said, had been linked by biometric data to the production or placement of improvised explosive devices (IEDs), sometimes through fingerprints left on adhesive tape used to assemble homemade bombs. (Additional reporting and writing by Missy Ryan; Editing by Paul Tait and Ron Popeski)