Allegations Iraqi prisoners of war were mistreated by UK troops are being investigated, after photographs allegedly showing the abuse were discovered.
The MoD says reports of abuse will be "thoroughly investigated"
A British soldier has been arrested on suspicion of taking the pictures, including one showing an Iraqi, bound and gagged, hanging from netting on a fork-lift truck.
Police were called in after the photographs were handed into a store in Tamworth, Staffordshire, for developing.
If the pictures are found to show real Iraqis, and have not been stage-managed, such treatment would be a breach of the Geneva Convention which governs the treatment of POWs, says the Ministry of Defence (MoD).
An MoD spokeswoman said an investigation into the allegations was under way.
"We can confirm that an investigation is being conducted into allegations that a soldier took photographs depicting mistreatment of Iraqi POWs.
"We cannot comment further. But if there is any truth in these allegations the MoD is appalled.
"We take responsibility to POWs extremely seriously.
THIRD GENEVA CONVENTION
Basic food rations should keep prisoners in good health
Suitable clothing should be supplied, preferably prisoners' original uniforms
Prisoners must be protected against violence or intimidation, insults and public curiosity
POWs should be released and repatriated after ceasefire
"The Geneva Convention makes clear that 'prisoners of war are entitled to respect to their persons and their honour'.
"Any allegation that this has been breached must be seriously and thoroughly investigated.
"The individual concerned was arrested yesterday by Staffordshire Police and is in custody."
Lesley Warner, from Amnesty International, said: "If these allegations are true they are very clearly against the Geneva Convention.
"There is no doubt at all if prisoners of war were suspended from a net it is clearly degrading treatment and it should be investigated thoroughly."
The pictures are believed to have been taken by a soldier serving in the 1st battalion Royal Regiment of Fusiliers - part of the 7th Armoured Brigade, nicknamed the Desert Rats.
The pictures were handed into a store in Tamworth
The soldier - whose rank has not been disclosed - lives in Staffordshire.
Colonel Bob Stewart, former army officer, said: "If someone has done this then it devalues the British Army which is a great pity.
"That's why the British Army understands that if there's an accusation it must be rigorously pursued and proved either guilty or not guilty."
An investigation is already under way into allegations that Colonel Tim Collins, former commanding officers of the 1st Royal Irish Regiment, mistreated Iraqi civilians and prisoners - although the two cases are not linked.
Col Collins has strongly denied the claims.