BEIJI, Iraq (AP) -- A group of American soldiers in an insurgent-riddled town allegedly noticed a young Iraqi woman when on patrol and later returned to rape her, according to U.S. officials. In an apparent cover-up attempt, she and three members of her family then were killed and her body was set on fire.

Five U.S. troops are being investigated, a U.S. military official told The Associated Press.

It is the fifth pending case involving alleged slayings of Iraqi civilians by U.S. troops.

The suspects in the killing, which took place in March, were from the same platoon as two soldiers kidnapped and killed south of Baghdad this month, said the official, who is close to the investigation and spoke on condition of anonymity because of the sensitivity of the case.

One soldier was arrested after admitting his role in the alleged attack on the family, the U.S. official said. The official said the rape and killings appear to have been a "crime of opportunity," noting that the soldiers had not been attacked by insurgents but had noticed the woman on previous patrols.

One of the family members they allegedly killed was a child, said a senior Army official who also requested anonymity because the investigation is ongoing. Some of the suspects allegedly burned the woman's body to cover up the attack, the U.S. official said.

In Baghdad, the U.S. military issued a sparse statement, saying only that Maj. Gen. James D. Thurman, commander of the 4th Infantry Division, ordered a criminal investigation into the alleged slaying of a family of four in Mahmoudiya, 20 miles south of Baghdad.