BAGHDAD, Iraq — An American soldier testified yesterday that comrades threatened to kill him if he disclosed their roles in the slaying of three Iraqi detainees in May in northern Iraq.

Private First Class Bradley Mason, 20, said at a military hearing in Tikrit that Staff Sergeant Raymond Girouard threatened him on May 10, the day after the Iraqis were shot dead in a raid on a suspected base of the insurgent group Al Qaeda in Iraq near Samarra, about 65 miles north of Baghdad.

“He said that if I say anything, he’d kill me,” Private Mason said, according to a pool report.

Later that day, Private Mason said, Private First Class Corey Clagett told him Sergeant Girouard “won’t have to kill me because he’ll kill me.”

The case is one of several to surface in recent months in which American service members have been accused of wrongfully killing Iraqi civilians, including an alleged massacre in Haditha and charges that five American soldiers raped and murdered a 15-year-old girl near Mahmoudiyah. The allegations have prompted strong denunciations from Iraqi leaders and critics of the American military presence here.

Sergeant Girouard, Private Clagett, Specialist William Hunsaker, and Specialist Juston Graber have all been charged with murder and other offenses in connection with the killing of the three Iraqis. All but Specialist Graber are also charged with obstruction of justice for allegedly threatening to kill Private Mason.

All of the accused are members of the Army’s 3rd Battalion,187th Infantry Regiment, 101st Airborne Division.

Private Mason delivered his testimony during a so-called Article 32 hearing, after which a military court will rule whether there is sufficient evidence to court-martial the four defendants. A witness for the prosecution, Private Mason was granted immunity to testify.

Private Mason testified that, during the May 9 raid, Sergeant Girouard told his squad that Private Clagett and Specialist Hunsaker were going to kill three detainees who had been handcuffed.

Private Clagett and Specialist Hunsaker “just smiled,” Private Mason said, adding that he objected to Sergeant Girouard. “I told him I’m not down with it. It’s murder,” he said.

Shortly afterward, Private Mason said, he heard the sound of gunfire. The three detainees were dead, he said, and Private Clagett told him that two had broken out of their plastic cuffs.

Private Mason, who acknowledged that he killed an “old man” during the raid, also stated that his unit — the 3rd Battalion’s C Company — had been told to kill any military-age Iraqis it encountered.

Another witness, First Lieutenant Justin Werheim, testified soldiers were told “several times” to “positively identify and kill any military-age male on the island” in Tharthar Lake where the raid was carried out.

Private First Class Jason Joseph, however, testified the soldiers’ orders were to “kill all military-age males that were not actively surrendering.”

The hearing, which opened Tuesday, may continue for several more days.

In Baghdad, meanwhile, explosions killed civilians in several neighborhoods yesterday.

The deadliest killed 11 Iraqis in the evening on a makeshift soccer field in west Baghdad, news services reported. Police said the victims, between the ages of 15 and 25, were killed by two bombs buried in the field.

Three roadside bombs exploded yesterday at Baghdad’s al-Tayiran Square, killing five people and wounding 11.

In western Iraq’s Anbar province, two American service members were killed in combat, the military said. One was a Marine attached to the Army’s 1st Armored Division, the other a soldier assigned to the 9th Naval Construction Regiment.