BAGHDAD, Iraq – Residents gave new details yesterday about the shootings of civilians in a western Iraqi town, where the American military is investigating allegations of potential misconduct by American troops last November.

The residents said troops entered homes and shot and killed 15 members of two families, including a 3-year-old girl, after a roadside bomb killed an American Marine.

The military, which announced Friday that a dozen Marines are under investigation for possible war crimes in the November 19 incident, said in a statement yesterday that a videotape of the aftermath of the shootings in Haditha, 140 miles northwest of Baghdad, was presented in support of the allegations.

The charges against the Marines were first brought forward by Time magazine, which reported this week that it obtained a videotape two months ago taken by a Haditha journalism student that shows the dead still in their nightclothes.

The magazine report mirrored what was told independently to the Associated Press by residents who described what happened as “a massacre.” However, Time said the available evidence did not prove conclusively that the Marines deliberately killed innocents.

A military spokeswoman said yesterday the allegations were being taken “very seriously.”

Khaled Ahmed Rsayef, whose brother and six other relatives were killed, said the roadside bomb exploded at about 7:15 a.m. in the al-Subhani neighborhood, heavily damaging an American Humvee.

An American military statement in November described it as an ambush on a joint American-Iraqi patrol that left 15 civilians, eight insurgents, and an American Marine dead in the bombing and a subsequent firefight. The statement said the 15 civilians were killed by the blast, a claim residents denied.

The residents said the only shooting done after the bombing was by American forces.

“American troops immediately cordoned off the area and raided two nearby houses, shooting at everyone inside,” Mr. Rsayef, who did not witness the events but whose 15-year-old niece says she did, said. “It was a massacre in every sense of the word.”

Mr. Rsayef and another resident, former city councilman Imad Jawad Hamza, who spoke with hospital officials and residents, said the first house to be stormed was that of Abdul-Hamid Hassan Ali, which was near the scene of the bombing.

Ali, 76, whose left leg was amputated years ago because of diabetes, died after being shot in the stomach and chest. His wife, Khamisa, 66, was shot in the back. Ali’s son, Jahid, 43, was hit in the head and chest. Son Walid, 37, was burned to death after a grenade was thrown into his room, and a third son, 28-year-old Rashid, died after he was shot in the head and chest, Messrs. Rsayef and Hamza said.

Also among the dead were son Walid’s wife, Asma, 32, who was shot in the head, and their son Abdullah, 4, who was shot in the chest, Messrs. Rsayef and Hamza said.

Walid’s 8-year-old daughter, Iman, and his 6-year-old son, Abdul-Rahman, were wounded and American troops took them to Baghdad for treatment. The only person who escaped unharmed was Walid’s 5-month-old daughter, Asia. The three children now live with their grandparents, Messrs. Rsayef and Hamza said.

Mr. Rsayef said those killed in the second house were his brother Younis, 43, who was shot in the stomach and chest, the brother’s wife Aida, 40, who was shot in the neck and chest while still in bed. Their 8-year-old son Mohammed bled to death after being shot in the right arm, Mr. Rsayef said.

Also killed were Younis’s daughters, Nour, 14, who was shot in the head; Seba, 10, who was hit in the chest; Zeinab, 5, shot in the chest and stomach, and Aisha, 3, who was shot in the chest. A visiting relative, Hoda Yassin, was also killed, Messrs. Rsayef and Hamza said.

The only survivor from Younis’s family was his 15-year-old daughter Safa, who pretended she was dead. She is living with her grandparents, Mr. Rsayef said.

The troops then shot and killed four brothers who were walking in the street, Messrs. Rsayef and Hamza said, identifying them as the sons of Ayed Ahmed – Marwan, Qahtan, Jamal, and Chaseb.