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Suicide bombers driving trucks laden with chlorine have launched three attacks in Iraq that exposed hundreds of people to the potentially deadly gas.
The attacks were a dramatic challenge to the security crackdown by the United States Army and the Iraqi Government aimed at introducing a measure of stability.
US officials had been guardedly positive that the "surge" of new troops was reducing violence, especially in Baghdad. "We are, if anything, cautiously optimistic," said military spokesman Lieutenant Colonel Christopher Garver.
But the chlorine attacks showed that insurgents still have the power to terrify. The first truck exploded in Ramadi and was followed by two more south of Fallujah.
In each, a truck loaded with canisters of chlorine gas was exploded.
The attacks killed at least two policemen and injured 350 civilians, including dozens of children. Six US soldiers were taken to hospital.
Chlorine gas irritates the skin and the lungs, causing intense pain and organ damage. It causes severe burns when inhaled and can cause death.
The tactic was first used by insurgents in January, when two bombs with chlorine killed eight people.
The chief US military spokesman in Iraq, Major General William Caldwell, has called the new tactics a "crude attempt to raise the terror level".
Chlorine attacks kill fewer people than conventional suicide bombs but they are especially frightening to an Iraqi population whose memory of gas attacks during the Iran-Iraq war remains fresh.
The latest attacks took place in the restive Sunni province of Anbar and may confirm what many fear - that the security crackdown in Baghdad has forced insurgents further afield.
At the same time, the US has been successful in persuading some local Sunni leaders to fight al Qaeda groups in Anbar, causing an upsurge in violence in the province.
Another car bomb exploded in Fallujah on Saturday, aimed at a tribal leader who had denounced al Qaeda.
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