A four-member team from the International Committee of the Red Cross is continuing to interview suspected al-Qaida members detained at the makeshift American detention centre in Cuba.
Human rights activists want the US government to classify the captives as prisoners of war.
The US, which maintains the prisoners - who have yet to face any charges - are being treated humanely, refuses to call them PoWs, referring to them rather as "illegal combatants".
Under the Geneva Convention, PoWs must be tried by the same courts and under the same procedures as US soldiers.
Under that status, prisoners would be tried for war crimes through courts-martial or civilian courts, not by secretive military tribunals which could impose the death penalty.
The US military has already brought more than 100 captives from Afghanistan to Guantanamo in Cuba.
The temporary camp will soon be able to hold 320, or more if they are housed two to a cell.
Workers are building a permanent prison for up to 2,000.
The US is still holding more than 300 prisoners in Afghanistan, at the Marine base at Kandahar airport, and a few others elsewhere.
British MPs are seeking a meeting with the US ambassador over the treatment of the detainees - including three British citizens.