BAGHDAD, Iraq — A string of bombings killed at least 15 people today in the Baghdad area, a day after a massive car bomb attack in a Shiite area market delivered the first major blow to the U.S.-led security crackdown.

Attacks in other parts of Iraq pushed the overall death toll near 30.

U.S. forces also reportedly came under attack. They clashed with insurgents north of Baghdad after a suicide bomber apparently tried to break through barriers around a joint U.S.-Iraqi base, area residents said. U.S. military officials said they were looking into the incident.

In Baghdad, five people were killed when a suicide attacker detonated a bomb-rigged belt on a public bus headed for the mostly Shiite area of Karradah in central Baghdad, police reported.

A roadside bomb killed three policemen in the Shiite area of Zafraniyah, officials said. Only 100 yards away, a bomb hidden in an open-air market exploded, killing at least five.

In Mahmoudiya, a car bomb went off among auto repair shops, killing two and wounding two, police said. Mahmoudiya is mostly Shiite with Sunnis living in villages around the community and has long been a flashpoint for sectarian violence.

Elsewhere in Iraq, a car bomb in Ramadi killed at least nine bystanders congregated at a police checkpoint in the aftermath of a failed suicide attack.

Meanwhile, the U.S. military announced Monday that a U.S. Marine was killed two days earlier during combat operations in Anbar province, a Sunni insurgent hotspot west of the capital.