6 . By letter dated 20 July 2004 , the Permanent Mission of the United Kingdom of Great Britain and Northern Ireland to the United Nations Office at Geneva submitted a response explaining the three distinct categories of persons detained by United Kingdom troops in Iraq : prisoners of war ( POWs ) held under the Geneva Convention relative to the Treatment of Prisoners of War ( Third Geneva Convention ) ; security internees held under the Geneva Convention relative to the Protection of Civilian Persons in Time of War ( Fourth Geneva Convention ) and criminal detainees .