British troops are under criminal investigation over the detention of Iraqis in Basra 13 years ago.
The probe is focused on allegations of ill-treatment of two Iraqis who were accused of involvement in the deaths of two British soldiers during the conflict.
Staff Sergeant Simon Cullingworth and Sapper Luke Allsopp were killed in 2003.
The two British bomb disposal officers were captured when their convoy was ambushed by militiamen, and they were taken to a military intelligence compound where they were shot dead.
Faisal al-Saadoon and Khalaf Mufdhi were detained by British forces and held for "imperative reasons of security".
The Government was found guilty in 2010 of exposing the two Iraqis to years of fear of execution, in breach of their human rights.
In May 2006, the Iraqis were charged with murder and war crimes, but the Iraqi High Tribunal (IHT) later annulled the charges against the men due to insufficient evidence.
Now, the Iraq Historic Allegations Team (Ihat) - which was set up in November 2010 to look into allegations of murder, abuse and torture of Iraqi civilians by UK military personnel between 2003 and 2009 - has said it is looking into allegations of ill-treatment.
It is not known how many British troops are under investigation.
An Ihat spokesman said: "I can confirm that Ihat is investigating allegations that al-Saadoon and Mufdhi were ill-treated while in custody. The allegations were brought to our attention by PIL."
It was Public Interest Lawyers (PIL), a firm focusing on human rights cases, which in 2008 stepped in to fight in the UK courts against the two men's transfer to the Iraqi authorities, on the grounds that they faced the risk of an unfair trial and death by hanging if convicted.
Theresa May last month raised concerns over the "industrial scale" of claims lodged with Ihat, which has considered claims relating to more than 1,500 individuals, ranging from ill-treatment during detention to assault and death by shooting.
Some 326 cases have been settled, with the payment of around £20 million in compensation, but concerns have been raised about servicemen facing investigation even after having been cleared of wrongdoing by criminal courts.
A Government spokeswoman said: "We've seen our legal system abused to falsely impugn our armed forces and we are putting an end to that.
"Equally, our armed forces are rightly held to the highest standards and, whilst rare, where there are credible claims of criminal behaviour, we should investigate them.
"Stamping out the many spurious claims will mean Ihat is better able to focus on the few credible ones."