BAGHDAD, Iraq — A U.S. Army staff sergeant has been charged with premeditated murder in the deaths of two soldiers — including the suspect's commanding officer — this month at their base outside the city of Tikrit, military officials said today.

The two suffered fatal wounds in a series of June 7 explosions that struck as they conferred in a room on a base, situated on the compound of a former palace of Saddam Hussein. The two officers died the next day. Officials initially reported that the explosions were mortar strikes.

The charges against Staff Sgt. Alberto B. Martinez, 37, are believed to represent the first suspected case of "fragging," a military term for the killing of an officer by a subordinate, in Iraq. Allegations of fragging, so named because hand grenades, known to troops as frags, became infamous during the Vietnam War, when some discontented U.S. troops turned on their superiors.

Authorities did not talk about a possible motive in the Iraq case, saying that a criminal investigation is continuing. But authorities indicated that Capt. Phillip T. Esposito, who was Martinez's commanding officer, was believed to be the target of the explosions.

Esposito was commander of Headquarters and Headquarters Co. for the 42nd Infantry Division, a New York Army National Guard unit. It provides logistics and support to the division commander and his staff.

Esposito, 30, a 1997 graduate of West Point, was the father of an 18-month-old daughter.

The Army would not comment on whether Martinez was facing disciplinary action at the time of the deaths.

Also killed was the company operations officer, 1st Lt. Louis E. Allen, 34, a father of three from Milford, Pa. Allen had only recently arrived in Tikrit, one official said, and may have simply been in the wrong place at the wrong time.

42nd Infantry Division arrived in Iraq in January. It patrols a broad swath of northern Iraq, including extremely dangerous stretches of the nation's Sunni Arab heartland where the insurgency is raging. Its base along the Tigris River at one of Hussein's former palaces is known as Forward Operating Base Danger.

Reports about the two deaths have reached the highest levels of the U.S. military in Iraq, where more than 1,700 U.S. troops have died in a war that polls suggest is becoming increasingly unpopular with the American public. Insurgents seeking to oust U.S. forces launch daily attacks on the troops and their allies in the new Iraqi government.

The military's initial account that Esposito and Allen had died in a mortar attack was retracted after experts determined that the blast pattern was inconsistent with a mortar shell or rocket. The two men reportedly were in a first-floor room when the explosions struck.

The families first were told that the men had died in an insurgent strike, the Army said. But both families were contacted again when evidence showed otherwise, the Army said.

Military spokesmen would not comment publicly on the kind of explosive involved. But one knowledgeable source indicated that hand grenades and a claymore mine — an anti-personnel mine that scatters deadly pellets when detonated — may have been utilized. Authorities say they believe there were four explosions.

The lavish building where they were killed is known as the Water Palace because of its location beside a small lake at the base.

Martinez is being held at a military facility in Kuwait, the Army said.

An official said Martinez is believed to have acted alone. If convicted of the charges, he could face capital punishment.

The Army has provided legal counsel to Martinez, the military said. "Staff Sgt. Martinez has seen and will continue to be afforded the extensive rights under the Uniformed Code of Miliary Justice," said Col. Billy J. Buckner, spokesman for the Multi-National coalition here.

The criminal case against Martinez is not the first time such allegations have been made against an American soldier in the Iraq conflict.

In April, a military jury at Fort Bragg, N.C., convicted Army Sgt. Hasan Akbar of murder in the killing of two fellow soldiers in a grenade and rifle attack at his camp in Kuwait in March 2003, early in the U.S.-led invasion of Iraq. The attack wounded 14 other troops.

Akbar was the first U.S. service member to be court-martialed on murder charges in the wartime killing of comrades since the Vietnam War era.