Nine U.S. soldiers have officially become casualties of the war in Iraq, one dying in a grenade attack in Kuwait, one in a vehicle accident in southern Iraq, five in helicopter crashes and two in ground operations.

One soldier was killed and 15 injured Sunday in a grenade attack, for which a U.S. soldier was being held as a suspect.

-- Army Capt. Christopher Scott Seifert, 27, was killed by the grenade. He was assigned to the 1-101st Airborne Division at Fort Campbell, Ky.

A serviceman from the 3rd Infantry Division died in a vehicle crash in southern Iraq.

A U.S. Navy officer and six British troops were killed Saturday when two British Royal Navy helicopters collided over the Persian Gulf.

-- U.S. Navy Lt. Thomas Mullen Adams, 27, of La Mesa, Calif. was killed in the collision. He had been assigned as an exchange officer with the Royal Navy's 849th Squadron since October 2002.

Two Marines that were based at Camp Pendleton, Calif., were killed Friday in ground fighting as U.S. and British forces overtook the town of Safwan in southern Iraq and the strategic Persian Gulf port of Umm Qasr en route to Baghdad.

-- Lance Cpl. Jose Gutierrez, 22, of Los Angeles, assigned to the 2nd battalion, 1st Marine regiment, of the 1st Marine Division.

-- 2nd Lt. Therrel S. Childers, 30, of Harrison, Miss., with the 1st battalion, 5th Marine regiment, of the 1st Marine Division.

A U.S. Marine helicopter carrying eight British and four U.S. soldiers crashed in Kuwait Friday, killing everyone on board, the Pentagon said. The CH-46 Sea Knight helicopter assigned to the 1st Marine Expeditionary Force crashed at 7:37 p.m. EST (Friday morning in Kuwait), about nine miles away from the border with Iraq, military officials said.

The cause of the crash is under investigation, the officials said, adding that hostile fire had not been reported in the area.

Among those who died in the crash were:

— Three Marines based out of Camp Pendleton, Calif.:

Marine Ryan Beaupre, 30, of St. Anne, Ill. Beaupre piloted the CH-46, according to his sister, Alyse.

Kendall Damon Waters-Bey, 29, of Baltimore, a specialist in helicopter maintenance. He was assigned to the Marine Medium Helicopter Squadron-268, Third Marine Aircraft Wing.

Cpl. Brian Kennedy, a Texan whose mother lives in Port Clyde, Maine.

—- The other Marine killed in the crash was identified as Capt. Jay Aubin of Waterville, Maine, who was based at Marine Corps Air Station Yuma.

Fox News' Amy Sims and The Associated Press contributed to this report.