Three trucks rigged with chlorine bombs exploded in the insurgent stronghold of Anbar province Friday, in the latest efforts by insurgents to use the toxic chemical to boost the lethal power of their attacks, U.S. military officials announced Saturday.

The U.S. officials said at least 350 people and seven U.S. soldiers were injured and two policemen were killed in the attacks. As many as 10 civilians may have been killed in two of the blasts near Fallujah, said Col. Sami Jabara, a spokesman for the Ministry of the Interior.

The first in the trio of chemical-releasing bombs detonated shortly after 4 p.m. at a checkpoint near Ramadi, west of Baghdad. It injured one American soldier and one Iraqi civilian.

About two hours later, a second blast 10 miles south of Fallujah killed two policemen and exposed as many as 100 residents to chlorine fumes, the military said in a statement. The civilians were treated for skin and lung irritation, vomiting, and other injuries.

Thirty-seven minutes later, a dump truck carrying a 200-gallon chlorine tank strapped with explosives blew up three miles south of Fallujah. At least 250 people were injured, the military said.

Friday's attacks were the latest in a string of bombings this year in which insurgents laced bombs with chlorine to boost their lethality. In February, insurgents blew up a truck transporting chlorine gas tanks in Taji, north of Baghdad, killing nine people. In January, another truck carrying explosives and chlorine tanks exploded near Ramadi, killing 16 people.

After last month's attack, American forces who raided a car bomb factory near Fallujah discovered several buildings packed with bomb supplies, including chlorine cylinders and other chemicals.

Suicide car bombers have used chlorine against Iraqis in Anbar province a total of five times since Jan. 28, the military said today.