BAGHDAD, Iraq — U.S. Marines killed five insurgents and captured 10 others in a city west of Baghdad as American forces there stepped up their campaign to suppress deadly roadside bombs, the U.S. military said today. Roadside bombs killed at least seven Iraqi security troops across the country.

Four Americans, meanwhile, died Monday evening in a suicide car bombing in southwestern Baghdad, the military said. A civilian translator was also killed.

According to a military statement, the five insurgents died Monday in Ramadi, 70 miles west of Baghdad, in a series of shootings that began when Marines discovered their attempts to plant bombs in a hole used by militants in the past to conceal explosives.

The incident occurred one day after Army snipers killed eight insurgents who were also trying to conceal explosives in Ramadi, capital of Iraq's most volatile province, Anbar.

Roadside bombs have become the major killer of American forces in Iraq, accounting for most of the 96 deaths last month.

Four Iraqi soldiers, including a major, were killed by a roadside bomb in Khalis, 35 miles north of Baghdad. To the south, a senior member of the Iraqi police in Basra, Col. Mahmoud Qassim, was killed by a bomb south of the city, police said. Another policeman also died in the attack.

A roadside bomb also killed a policeman and wounded three others today near the northern oil city of Kirkuk.

The U.S. military released few details about the deaths of the four Americans and their translator. They were members of the U.S. Army's Task Force Baghdad and were killed about 5 p.m. Monday.