The Pentagon announced Tuesday that it has transferred 18 detainees at the US naval base prison in Guantanamo Bay, Cuba, to Afghanistan and Turkey for release.

Seventeen of the detainees were transferred to Afghanistan and the remaining one was transferred to Turkey, the Pentagon said in a statement.

"This transfer includes 18 detainees found to no longer be an enemy combatant by a Combatant Status Review Tribunal," the statement said.

With Tuesday's transfer, a total of 232 detainees have left Guantanamo, leaving some 520 Taliban and al Qaida suspects at the detention facilities there. Of those who have left Guantanamo, 65 were transferred to the custody of other countries, and at least 10 who were set free 10 had rejoined the fight against US forces.

At its peak, there were more than 750 prisoners at Guantanamo, most of whom were captured during the US-led war in Afghanistan.

The Pentagon initially declared that all detainees at Guantanamo were "enemy combatants" and could be held indefinitely without charges, rather than prisoners of war who would have the right to protection under the Geneva Conventions.

A Pentagon review over their status, which started in July last year, has decided that 38 prisoners at Guantanamo were no longer considered "enemy combatants" and would be set free.