The United States and Britain suffered their first casualties as they pushed into Iraq, with two U.S. Marines killed in combat and 19 more American and British Marines dying in helicopter crashes that appeared to be accidental.

A U.S. Marine was the first to die in action. His company was advancing on a burning oil pump station when he was shot in the stomach, a comrade said. President Bush was informed of the death early Friday and expressed his regrets.

He was from the U.S. 1st Marine Expeditionary Force, said Lt. Col. Neal Peckham, a British military spokesman in Kuwait. He died in the sweep on the Rumeila oil field in southern Iraq, where acrid smoke blackened the sky.

U.S. Central Command gave no other details.

The second Marine, also from the 1st Marine Expeditionary Force, died Friday at about 4 p.m. while fighting enemy Iraqi forces near Umm Qasr, a strategic port which came under allied control Friday.

Eight British and four U.S. Marines died when their CH-46 Sea Knight helicopter crashed and burned about nine miles south of the Iraqi border town of Umm Qasr. Military officials said no hostile fire was reported in the area.

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

The Pentagon identified the four Marines killed in the Sea Knight crash as Maj. Jay Thomas Aubin, 36, of Waterville, Maine; the pilot, Capt. Ryan Anthony Beaupre, 30, of Bloomington, Ill.; Cpl. Brian Matthew Kennedy, 25, of Houston; and Staff Sgt. Kendall Damon Waters-Bey, 29, of Baltimore.

Aubin's unit was from Yuma, Ariz., while the other three were based at Camp Pendleton, Calif.

At a Washington news conference, Defense Secretary Donald Rumsfeld expressed gratitude for their sacrifice.

"The world will be a safer place because of their dedicated service," he said.

In Illinois, Alyse Beaupre, 31, said her brother was a graduate of Illinois Wesleyan University and a member of the Roman Catholic church in St. Anne's, about 60 miles south of Chicago.

University registrar Jack Fields said he was surprised when the young man with the shock of unruly red hair enlisted in the Marines.

"The image that comes to mind is from 'The Andy Griffith Show,' and Opie walking down the road with a fishing pole," he said.

But Alyse Beaupre said, "He always wanted to fly."

Waters-Bey was the only son among five children in his family; he was married to a woman who serves in the Navy, and had a 10-year-old child from a previous marriage.

Speaking from his Baltimore home, his father, Michael, said he did not support the war. Asked what he would tell President Bush, he said: "This was not your son or daughter. That chair he sat in at Thanksgiving will be empty forever."

He said the holiday last year was the last the family saw Waters-Bey, who grew up in a working-class neighborhood and excelled in swimming and track in high school.

"I was devastated. My only son, my first-born, gone," the father said as family members huddled on a couch, smiling and crying as they leafed through photographs to remember the Marine.

Aubin's mother, Nancy Chamberlain, said her son enlisted in the Marines and served four years before leaving for college. After he attended the University of Southern Maine, the Marines contacted him to see if he was interested in rejoining.

"To be a pilot -- that's all he really wanted to do," said Aubin's cousin, Colby Willett, 24, of Portland, Maine. "He was a lifer and he really believed in everything he was doing over there."

As talk of war began, Aubin knew he would probably be among the first to enter combat, according to his father, Tom, and stepmother, who live in the central Texas town of Bangs. He asked his stepmother to protect his father, who has a bad heart.

"He told me this summer, don't tell this to dad, but if something starts up, I'll be right in the thick of it," Carol Aubin told The Associated Press.

Jay Aubin was married and had a daughter, 10, and a son, 7.

Kennedy graduated from high school in Glenview, Ill., with honors in 1995, then attended Purdue University before transferring to Texas Tech in 1998, according to his father. He enlisted the next year.

"He gave his life in an effort to contribute to the freedom of the Iraqi people," Mark D. Kennedy, 52, said Friday from his Houston home.