The Pentagon has said it is holding 7,000 POWs, while Britain has said it has 6,500.
The United States has already opened one so-called Theatre Internment Facility designed to house 4,000 prisoners at an undisclosed location in southern Iraq.
The site is expected to expand to accommodate a further 4,000 prisoners next week.
Unlawful combatants: Usually guerrillas operating outside the regular armed forces.
US military spokesman Commander Chris Isleib told BBC News Online: "We're treating all prisoners as POWs until they receive further designation."
"The priority is to get them away from the battlefield, see to their humanitarian needs and then identify them. POWs receive medical treatment as needed," he added
The Geneva Convention entitles all prisoners taken in war to food, shelter, medical treatment, visits from relief agencies and other rights.
3rd GENEVA CONVENTION
Basic food rations should keep prisoners in good health
Suitable clothing should be supplied, preferably prisoners' original uniforms
Prisoners should be released and repatriated without delay after ceasefire
Prisoners to be protected from violence or intimidation and against "insults and public curiosity"
The International Committee of the Red Cross (ICRC) which monitors POWs around the world, says it has inspected one camp in southern Iraq and started registering prisoners.
The ICRC says its chief concern is to ensure the prisoners' humane treatment, inspect their living conditions, inform relatives of their status and arrange for exchanges of news between POWs and their families.
According to the Geneva Convention, prisoners can be questioned by their captors, but are only obliged to give their name, rank and serial number.
Another section of the convention states that "prisoners of war must at all times be protected... against acts of violence or intimidation and against insults and public curiosity."
Shielding POWs from "public curiosity" lies at the heart of one of the most contentious issues of the war: the broadcast of pictures of captured soldiers from both sides on television.
Psychologically and politically, images of surrendering or captured soldiers are extremely valuable.
In the initial stages of the war, Washington hoped that news footage of the mass surrender of Iraqi troops would encourage others to follow suit, and prompt the swift collapse of the regime.
Arguably, however, the POW footage which has had the greatest impact during the war so far has been that of bewildered American prisoners being questioned on Iraqi state television.
These scenes triggered shock and anger in the United States - and accusations that Iraq, and news organisations which broadcast the footage had broken the Geneva Convention.
Rules of engagement
For its part, the US has indicated that it may prosecute irregular Iraqi forces for action against US troops which Washington argues has broken international rules of engagement.
Throughout the war, the US has reported a series of incidents in which its soldiers have come under fire from Iraqi soldiers and irregular forces dressed in civilian clothes, wearing civilian clothes over uniforms, or faking a surrender.
Washington - supported by many leading human rights groups - is also expected to press for the prosecution of senior figures in the Iraqi regime allegedly involved in human rights abuses.
However, deciding how such trials would take place and under what jurisdiction, legal experts say, could be a long and complicated process.
Alleged war criminals could face either a military court-martial, a military tribunal, a special international court or a specially arranged civilian court.