The Marines, who were assigned to the Regimental Combat Team 7, died Saturday. Their identities were not released.
At least 2,577 members of the U.S. military have died since the war began, according to an Associated Press count.
Also Sunday, a U.S. plane launched an airstrike against a building used by al Qaeda in Iraq, killing two militants, the U.S. military said. A car bomb exploded near the U.S. consulate in Kirkuk, killing two Iraqis and wounding seven others, Iraqi police said.
Four suspects were detained after the air attack, which took place southwest of Baghdad against extremists who had been staging mortar attacks on civilians, a U.S. statement said.
U.S. troops tracked the militants to a building and "coalition aircraft successfully executed the strike," the statement said.
The blast in Kirkuk near the consulate late Saturday was the seventh car bombing this month in the northern city, where tensions are rising among Arabs, Kurds and Turkomen over control of the area's vast oil wealth.
No Americans were injured, police Col. Burhan Tayeb said.
In other developments:
The U.S. command confirmed Saturday it is sending about 3,700 troops from elsewhere in Iraq to Baghdad to try to quell violence in the capital. The 172nd Stryker Brigade, which had been due to leave Iraq after a year's assignment, will be sent from the north to the capital, Gen. George W. Casey Jr., the top U.S. commander in Iraq, said. "Baghdad is a problem for us, there's no doubt about that. We are fighting Iraqis who are killing Iraqis," said Lt. Gen. Peter Chiarelli, commander, multi-national corps, told CBS News correspondent Mark Strassmann.
In Baghdad, Prime Minister Nouri al-Maliki warned television stations against broadcasting footage that could undermine the country's stability at a time of rising sectarian tensions. The U.S. military announced Saturday that it was moving 3,700 troops from Mosul to Baghdad to try to quell the sectarian violence sweeping the capital.
A statement by the prime minister's office cited news reports that "capitalize on the footage of victims of terrorist attacks." He called on media outlets to "respect the dignity of human beings and not to fall in the trap set up by terrorist groups who want to petrify the Iraqi people."
The statement said the government will take legal action against television stations that do not uphold the code of media ethics. The statement did not elaborate, but it fell short of an earlier al-Maliki warning that he will not hesitate to "shut them down if they do not stop inciting sectarianism."
There has been an increase in biased reporting by Shiite and Sunni television stations that focus on the suffering of their communities, often with little mention of the other.
In August 2004, the government closed the Baghdad news office of Al-Jazeera television, accusing the station of inciting violence. The office is still closed but the station operates in the Kurdish-ruled area of the north.
Earlier this month, in a visit to Kurdistan, al-Maliki refused to answer a question by an Al-Jazeera correspondent and reportedly rebuked Kurdish officials for allowing the network to operate there.
In November 2003, the U.S.-appointed Governing Council banned the Dubai-based Al-Arabiya television station from reporting from Baghdad after it aired an audio tape said to be from Saddam Hussein, who was still at large. The station was allowed to resume its work shortly afterward.