Baghdad: They have outraged Iraqis and been condemned by human rights groups, but next year the prisons in which U.S. forces hold thousands of Iraqis will be flung open under a U.S.-Iraq security pact.

That worries both the U.S. military, which fears hardened insurgents could again roam the streets, and rights campaigners who fear the opposite: that Iraqi authorities will transfer the detainees to Iraqi prisons -- and maybe torture or execute them.

"We are concerned that we will most likely release dangerous detainees back into the communities of Iraq who have directly contributed to the deaths of not only Iraqi and Coalition Forces, but countless numbers of civilians," said Major Neal Fisher, spokesman for U.S. detainee operations.

"Every detainee in our custody came to us because they posed an imperative threat to the security and stability of Iraq."

The security pact agreed with Iraq will give U.S. troops a legal basis to remain in the country for three more years, replacing a U.N. mandate that covered the presence of foreign forces in Iraq since the 2003 U.S.-led invasion.

For the first time, Iraq will have authority over roughly 150,000 U.S. troops in the country.

Iraq's presidency council ratified the pact on Thursday, bringing it formally into effect until a referendum in July.

One of the powers the U.S. military loses under the new deal is the right to detain Iraqis indefinitely without charge.

That means it will have to turn the 16,000-17,000 detainees currently in its custody over to Iraqi authorities in an orderly manner. Under Iraqi law, they will have to be tried or released.

For U.S. officials, that is a headache. Thousands of prisoners, some of them former Sunni Arab insurgents or Shi'ite militiamen, will be back on the streets. For most, there is simply not enough evidence to keep them under lock and key.

The U.S. commander in charge of the detainee program, Brigadier-General David Quantock, was unavailable for an interview, but he told USA Today that officials were working hard to build cases against dangerous detainees.

"We're going to... make sure they stay behind bars," he said.

Source : Reuters