Lawyers for five Iraqis are to publish evidence which they claim shows prisoners were executed by British troops.
Alleged survivors of the gun battle near the southern Iraqi town of Majat-al-Kabir in May 2004 will also claim that corpses were mutilated by UK military.
The allegations were first reported a month after the incident, known as the Battle of Danny Boy after a checkpoint where it took place, but lawyers claimed full details are about be published for the first time.
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The claims - which the Ministry of Defence (MoD) strongly denies - are among the most serious yet levelled against British soldiers who served in Iraq.
They will suggest that prisoners captured after the three-hour gun battle were taken to a British base at Abu Naji and killed.
Last month, the High Court heard in an application for a judicial review connected with the case that corpses showed signs of mutilation when they were removed from Abu Naji to a local hospital.
Death certificates written by Dr Adel Salid Majid, the director of the hospital to which the corpses were delivered, said the body of 37-year-old Ali al Jemindari had his right arm severed and an eye gouged out.
However, another doctor at the hospital said the injuries were consistent with a fierce gun battle, the court heard.
A spokesman for the MoD said: "Allegations of mistreatment, unlawful killing and mutilation by British troops following an incident at Vehicle Checkpoint Danny Boy were thoroughly investigated by the RMP.
"Their investigation found no evidence to support these allegations.
"New allegations are part of an ongoing RMP (SIB) investigation and judicial review and it would be inappropriate to comment further."
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