The U.S. military said Sunday it has ordered a criminal investigation into the June death of the 21-year-old cousin of Iraq's ambassador to the United Nations, who alleged that U.S. Marines killed his unarmed relative in cold blood during a raid in western Iraq.

Following a preliminary investigation, the case involving the death of Mohammed al-Sumaidaie has been referred to the Naval Criminal Investigative Service, or NCIS, for further investigation, the military said in a statement.

The NCIS is responsible for investigating alleged felony criminal offenses against people within the Department of the Navy, which includes the Marine Corps.

"At the conclusion of the investigation, a report will be provided to the command for review and further action as appropriate," the statement added.

Al-Sumaidaie was "killed during a search of his family's home near Haditha on June 25, 2005," the statement said.

Iraq's ambassador to the United Nations, Samir al-Sumaidaie (search), had demanded an investigation into his young cousin's death and punishment for the perpetrators. Mohammed al-Sumaidaie was an engineering student at the University of Technology in Baghdad.

In an e-mail to friends obtained by The Associated Press, the ambassador said his cousin was killed after he escorted Marines to a bedroom to show them where a rifle that had no live ammunition was kept.

When the Marines left, he was found in the bedroom with a bullet in his neck, the ambassador said.

The ambassador said the killing represented "a betrayal" of the values and aspirations of Iraqis and Americans to defeat the terrorists and build a country based on freedom, democracy and respect for human rights and the rule of law.

"It is a betrayal of the American people who are making huge sacrifices to bring this about, and a betrayal of Iraq and all Iraqi patriots who have put their trust in the United States," he said.

Iraqis often make allegations of mistreatment by U.S. troops during raids, and Haditha, 140 miles northwest of Baghdad, is a center of insurgent activity in Anbar province. Some troops have been court-martialed or are facing charges for misconduct.

However, few cases have drawn as much attention as the case of the younger al-Sumaidaie because of the ambassador's position. He was a former interior minister and served on the Iraqi Governing Council (search), which shared administrative responsibility with the U.S.-led coalition before sovereignty was transferred to the Iraqis in June 2004.

According to the ambassador, his cousin greeted the group of about 10 Marines and an interpreter who appeared to be Egyptian.

The Marines asked if there were any weapons, and Mohammed said there was a rifle, which only had blanks, the ambassador wrote. He then led some of the Marines into his father's bedroom where it was kept, al-Sumaidaie wrote.

A short time later, the young man's mother, brothers and sisters who were kept in the living room heard a thud, the ambassador said. Later a younger brother, Ali, was dragged by the hair into the corridor by a Marine and beaten. The mother started sobbing.

A Marine then went out and returned with a camera and went into the bedroom. After a while, the family went outside and waited on the porch as they were ordered, the ambassador said.

More than an hour later, as the soldiers were leaving, the interpreter asked the mother in Arabic if that was her son inside. When she replied "yes," the interpreter said, "they killed him," al-Sumaidaie said.