A roadside bomb exploded Saturday in the southern Baghdad neighborhood of Dora, killing three Iraqi soldiers, the army said.

At least one civilian was killed in fierce fighting between insurgents and the army in Fallujah, police Lt. Mohammed Khalaf said.

Fallujah, 40 miles west of Baghdad, was the country's main insurgent stronghold until U.S. forces overran the city in November 2004 in the most intense urban combat of the Iraq war.

In the southern city of Basra, four gunmen killed the director of traffic police as he was driving to work, police said. Basra is 340 miles southeast of Baghdad.

Meanwhile, two U.S. Marines were killed and 22 wounded — two of them critically — in fighting in western Iraq, the U.S. military said Saturday. 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 have already passed 40.