The Pentagon announced Tuesday that it has transferred four British detainees held at the US naval base prison in Guantanamo Bay, Cuba, to the custody of the British government.

With the transfer on Tuesday, 207 detainees have left Guantanamo so far, with 146 set free and 61 transferred to other countries for continued detention, leaving about 545 people still being held there, the Pentagon said.

Of those transferred for continued detention, 29 were handed over to Pakistan, nine to Britain, five to Morocco, seven to Russia, and four each to France and Saudi Arabia.

"The decision to transfer or release a detainee is based on many factors, including whether the detainee poses a continued threat to the United States or its allies and whether he is of further intelligence value," the Pentagon said in a statement.

During discussions between the Untied States and Britain, the British government requested the transfer of the four detainees and assured the US government that the detainees would not pose further security threat to the United States or its allies, the statement said.

The Pentagon initially declared all detainees at Guantanamo, most of whom were captured during the US-led war in Afghanistan, 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.