Tests have already been carried out by teams of specialist army investigators at Dover Air Force Base in Delaware on at least nine of the bodies.

An official said that X-rays, DNA tests and full body examinations had been completed on many dead servicemen. The results have been sent to the Armed Forces Institute of Pathology in Washington for analysis.

Parents and spouses of the dead soldiers, who had to give written permission for the tests, have been told that they will receive an official report within 60 to 90 days.

James Kiehl, 22, a computer engineer with the 507th Army Maintenance Division, is believed to have been killed in an ambush on March 23 near al-Nasiriyah.

His body was found in a shallow grave on April 2 outside the hospital from which a fellow soldier, Private Jessica Lynch, was rescued. His body was flown immediately, via Kuwait City, to Dover. His family, who live in Comfort, West Texas, were able to bury their son’s remains only on Monday because they had to wait for tests to be completed.

“We did have to wait what seemed like a very long time to get James back here,” Randy Kiehl, his father, said, “but we understand that the military has to do everything it can to find out exactly what happened to our son. I told them to take their time. It is better to know.”

Mr Kiehl, who is also a US Army veteran, is convinced that his son died honourably on the battlefield. He wanted the tests carried out, however, after seeing video footage from Iraq in which he believes he saw his son’s dead body, stripped of its uniform and marked with blood.

“Those images were horrible,” he said. “I would not let my wife see them. If the Iraqis that ambushed my son’s unit did anything wrong or committed any war crimes, I want it known about,” he said.

The US Defence Department accused the Iraqi Armed Forces of war crimes after viewing the same video footage, it is understood.

A spokesman for the Armed Forces Institute of Pathology said: “Our highly trained staff will look for specific injury patterns pertaining to the deaths of the servicemen. They will look for unusual types of body marks. Anything to help them discover the cause of death.”

The prisoners of war who were rescued, including Private Lynch, are also being asked to provide evidence of possible war crimes carried out by their captors.

At least five of the rescued soldiers were seen on another Iraqi videotape being questioned in circumstances US Army officials described as “under duress”.

A Pentagon official said that the tapes show “fundamental violations of the Geneva Convention obligations . . . against wilful killing, torture, inhumane treatment or the wilful causing of great suffering or serious injury to body or health of the PoW”.

The official added that the tape also showed captive soldiers “answering questions in humiliating and insulting circumstances designed to make them objects of public curiosity, in violation of the prisoner of war convention”.

It is unlikely that the US will seek prosecutions in the International Criminal Court at The Hague because neither it nor Iraq is party to the treaty that created the court.

The family of Ruben Estrella Jr, an 18-year-old soldier with the 507th who was killed at the same time as James Kiehl, were upset and angered by the delay in returning their son’s body.

“We were told three different dates for his return to El Paso,” Elsie Morgan, a spokeswoman for the family, said. “First the 8th, then the 10th and then he finally arrived back in El Paso on the 11th of April. Even then they changed the time of arrival by several hours, making meeting the body at the airport very difficult.”

Ruben Estrella’s remains were finally buried on Monday. “The family have had to endure feelings of annoyance because of all this. They were obviously upset,” she added.

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