MAHMUDIYA, Iraq (Reuters) -- The Iraqi woman at the centre of a rape-murder inquiry by the U.S. military was no more than 16 years old when she was killed along with her parents and young sister four months ago, the local mayor said on Monday.

The attackers, who U.S. commanders now suspect may have been American soldiers manning a checkpoint near the family home outside the town of Mahmudiya, then burnt the bodies to cover up the crime, mayor Muayyad Fadhil told Reuters in an interview.

"They were found killed and burnt on the morning of March 12," Fadhil said, just after he met a U.S. military officer at his municipal office in the small town south of Baghdad.

Hospital director Dawood al-Taie said his morgue received four burned bodies that day and showed death certificates made out on March 13 for the four named as the victims by the mayor.

"Gunshot to the head and chest. Face unrecognizable due to burns," read the certificate for Abeer Qasim Hamza, who the mayor said was 16 when she died and had been raped.

Taie said he had no record that evidence of rape was found.

The military has given few details of a probe launched a week ago after two soldiers came forward with allegations.

Officers said on Friday they were investigating whether at least three soldiers had a role in raping a woman at Mahmudiya and killing her and three relatives including a child on March 12. Troops originally blamed the killings on guerrilla fighters.

Somewhat conflicting versions of events are now emerging from local people in an area dubbed the "triangle of death".

Taboo

The accusations of rape, a taboo subject among rural Iraqi Muslims, may have contributed to a reluctance to publicize the killings -- one family member refused to discuss the issue on Monday and few Iraqi media have given coverage to the case.

But it also makes the case explosive for public opinion, even after a string of other charges being brought against U.S. troops as commanders crack down on misconduct toward civilians.

The Sunni Muslim Clerics Association said on Sunday the Mahmudiya case revealed "the real, ugly face of America".

Fadhil acknowledged it was a "dangerous subject" and said he had met a local U.S. commander to help complete the inquiry, which the mayor said he had been told was "75 percent complete".

"If it's true then it was a barbaric act of revenge against an area they call a 'hot spot' (of insurgent activity)," town council leader Najim al-Qaraawi said.

Anxious not to create new enemies and to leave behind a friendly Iraq when troops withdraw, U.S. commanders have issued orders to tighten up procedures on dealing with civilians.

Already tarnished by the Abu Ghraib prison abuse scandal in 2004, revelations in March of inquiries into the killing of 24 people at Haditha risk further damaging the U.S. image in Iraq.

Last month, 12 troops were charged with murder in two other cases, more than doubling the number of such charges in the war.

The mayor named the dead as Abeer Qasim Hamza, 16, who was raped, her father Qasim Hamza Rasheed al-Janabi, 38, mother Fakhriya Tahir Mheysin, 30, and sister Hadeel Qasim Hamza, 10.

The death certificates shown briefly by the hospital were numbered 579 to 582. Other details on the forms were unclear.

A U.S. military official said U.S. documents put the rape victim's age at 20, he said. He would not confirm other details of the case but said he was not aware of another in the area.

The Washington Post put the daughters' ages at 15 and 7. It quoted neighbor Omar Janabi saying Abeer Qasim's mother told him on March 10 the young woman had complained about advances made towards her by U.S. soldiers at a nearby checkpoint.

Janabi told the paper he was among the first to arrive at the house after an attack on March 11. He said he found Abeer sprawled dead in a corner, her hair and a pillow next to her consumed by fire.

The inquiry was launched after two soldiers from the 502nd Infantry Regiment came forward late last month. Two others are suspected of rape and one of these, since discharged from the army, is also suspected of the murders, officials said.