Baghdad, Iraq ? Three suicide bombers driving trucks rigged with tanks of toxic chlorine gas struck targets in heavily Sunni Anbar province including the office of a Sunni tribal leader opposed to al-Qaida. The attacks killed at least two people and sickened 350 Iraqi civilians and six U.S. troops, the U.S. military said Saturday.

There is a mounting power struggle between insurgents and the growing number of Sunnis who oppose them in Anbar, the center of the Sunni insurgency, which stretches from Baghdad to the borders with Syria, Saudi Arabia and Jordan. The Anbar assaults came three days after Prime Minister Nouri al-Maliki, a Shiite, traveled there to reach out to Sunni clan chiefs in a bid to undermine tribal support for the insurgency.

The violence started about 4:11 p.m. Friday when a driver detonated explosives in a pickup truck carrying chlorine at a checkpoint northeast of the provincial capital of Ramadi, wounding one U.S. service member and one Iraqi civilian, the military said in a statement.

Two hours later a dump truck exploded in Amiriyah, south of Fallujah, killing two policemen and leaving as many as 100 residents with symptoms of chlorine exposure ranging from minor skin and lung irritations to vomiting, the military said. Iraqi authorities said at least six people were killed and dozens wounded when the truck blew up in a line of cars waiting at a checkpoint. The U.S. did not confirm the Iraqi report.

Ahmed Kuhdier, a 32-year-old taxi driver, said the blast sent up a plume of white smoke that turned black and blue.

“Minutes later, we started to smell nasty smells. I saw people coming form the explosion site and they were coughing and having trouble breathing,” he said.

Another suicide bomber detonated a dump truck containing a 200-gallon chlorine tank rigged with explosives at 7:13 p.m. three miles south of Fallujah in the Albu Issa tribal region, the military said. U.S. forces found about 250 local civilians, including seven children, suffering from symptoms related to chlorine exposure, according to the statement. Police said the bomb was targeting the reception center of a tribal sheik who has denounced al-Qaida.

Four other bombings have released chlorine gas since Jan. 28, when a suicide bomber driving a dump truck filled with explosives and a chlorine tank struck a quick-reaction force and Iraqi police in Ramadi, killing 16 people. The U.S. military has warned that insurgents are adopting new tactics in a campaign to spread panic.