Baghdad, Iraq ? Two U.S. Marines were killed and 22 wounded – two of them critically – in fighting in western Iraq, the U.S. military said today. It was the biggest number of American casualties reported from a single engagement in weeks.

A U.S. statement said the casualties were suffered Thursday as a result of “enemy action” in Anbar province but gave no specific location or details of the fighting.

One Marine was killed “at the scene of the attack,” the statement said. Another Marine died at a medical facility in Taqqadum, it added.

Eight of the wounded were flown to the main U.S. hospital in Balad. Two were listed in critical condition and six were reported as stable, the statement said. The others were taken to a U.S. clinic at Camp Fallujah, where four were hospitalized for observation.

“Our hearts go out to the families of the dead and wounded Marines,” said Marine spokesman Lt. Col. Bryan Salas. “Our wounded Marines are receiving the best care available, and we look forward to their speedy recovery.”

U.S. casualties have begun to rise this month following a sharp drop in March, which saw the lowest number of American dead in Iraq since February 2004. Last month, 31 U.S. service members died in Iraq, but fatalities in April already have passed 40.

Meanwhile, dozens of Iraqi police remained missing and nine were dead after insurgents ambushed their convoy Thursday evening as they left a U.S. base where they had picked up new vehicles, Iraqi and U.S. officials said.

Brig. Gen. Abbas Maadal complained that the Americans refused to allow the police to spend the night at the base, just north of the capital. But U.S. spokesman Lt. Col. Barry Johnson said no such request had been made and that the Iraqis had not asked for American troops to guard the convoy.

The attack, the deadliest against police here in months, began about 7:30 p.m. Thursday as a convoy of 109 police traveled through a sparsely populated area near the Taji base heading back to Najaf, 100 miles to the south, Maadal said.

Police heard cries of “Allahu akbar,” or God is great, and “long live jihad” broadcast by loudspeaker from a nearby mosque, Maadal said. Suddenly insurgents, including some women, opened fire and triggered a roadside bomb.

Maadal said 37 policemen returned to Najaf late Friday and about 20 more were en route. About 40 remained unaccounted for. At least nine policemen were killed and three of the 12 vehicles were heavily damaged, Johnson said. One insurgent was wounded and five were arrested, he added.

Although no U.S. troops were with the Iraqi convoy when it came under attack, Johnson said American forces responded with helicopter gunships and ground troops.