The Ministry of Defence is probing claims an Iraqi prisoner of war was beaten to death by a British soldier.
Any unlawful action against PoWs would be dealt with, the MoD said
The MoD said the Royal Military Police was investigating the death of an Iraqi man while in British custody - thought to have happened in September.
The MoD said reports that a soldier could be charged with manslaughter were "pure speculation at this stage".
It is thought the man who died was taken prisoner during a raid on Pro-Saddam loyalists in Basra in the south.
The MoD said a full and thorough investigation was under way.
The Iraqi man who died is understood to be named Mr Al-Maliki.
Amnesty International Director Kate Allen said: "It is very important that there is an independent inquiry into the circumstances around his death."
There are unconfirmed reports the British soldiers were from the Queen's Lancashire Regiment near Basra.
An MoD spokeswoman said: "A Royal Military Police Special Investigations Branch investigation into the
death of Mr Al-Maliki is ongoing and it would be inappropriate to speculate
about its outcome.
"The investigation is a thorough one, involving interviews in Britain and
Iraq, and this inevitably will take time.
"If British soldiers are found to have acted unlawfully, appropriate action will be taken."
If the investigation reveals unlawful treatment of the Iraqis the soldiers could face full courts martial.