The most recent such attack occurred Feb. 21 in Baghdad, killing five people and sending more than 55 to hospitals, a day after a bomb planted on a chlorine tanker left more than 150 villagers stricken near Taji, 12 miles north of the capital.

A previously unannounced suicide car bombing in Ramadi involving chlorine killed two Iraqi security officers and wounded 16 other people, including 13 civilians, on Feb. 19, the military said Saturday.

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The military said last month that U.S. troops found a car bomb factory near Fallujah with about 65 propane tanks and ordinary chemicals it believed the insurgents were going to try to mix with explosives. Maj. Gen. William Caldwell, the chief U.S. military spokesman, called it a "crude attempt to raise the terror level."

Chlorine, which irritates the respiratory system, eyes and skin at low exposure and can cause death in heavier concentrations, is easily accessible. It is used for water purification plants, bleaches and disinfectants.

The primary effect of the chlorine attacks has been to spread panic. Although chlorine gas can be fatal, the heat from the explosions can render the gas nontoxic. Victims in the recent chlorine blasts died from the explosions, and not the effects of the gas.

Friday's strikes underscore the increasingly violent struggle for control of Anbar ¡ª a center for anti-U.S. guerrillas since the uprising in Fallujah in 2004 that galvanized the insurgency. In the past year, some major Sunni tribes have broken with the al-Qaida-linked insurgents ¡ª a move that has led to a new sense of optimism among U.S. officials in Anbar.

Al-Maliki on Tuesday made his first trip to Anbar province, meeting with influential clan chiefs whom the U.S. and the Iraqi government are cultivating. He expressed optimism the violence could be stopped and promised the area would not be forgotten as U.S. and Iraqi forces focus on a security sweep to stop the sectarian violence in Baghdad.

Bombings and shootings targeted police patrols elsewhere in Iraq Saturday, killing five policemen, including two who died after a suicide car bomber struck the checkpoint they were manning near a Sunni mosque in western Baghdad.

At least 34 other Iraqis were killed or found dead in attacks throughout the country, including five civilians shot to death in separate attacks in Diyala province northeast of the capital. Officials also said the director of the Sunni Endowment for mosques in Diyala, Fouad Mahmoud Attaya, was abducted earlier this week by gunmen in Baqouba and an investigation was under way.

A U.S. soldier was shot to death in fighting in the provincial capital of Baqouba, the military said. On Friday, a roadside bomb killed a soldier and wounded three others on a foot patrol south of Baghdad, the military said.

Gunmen abducted a radio newscaster and his driver in a predominantly Sunni neighborhood in western Baghdad, the station's director said.

Karim Manhal, a newscaster with Radio Dijla, and his driver were seized by four masked men in the Jami'a neighborhood near the station's headquarters, director Karim Yousif said. A female staffer who was with them in the car was released, he said.

Radio Dijla, named after the Arabic name for the Tigris River, was created in 2004 as Iraq's first independent talk radio station.

Protesters angry about U.S. policy in Iraq marched by the thousands in Washington and in smaller numbers in other U.S. cities and overseas ahead of Tuesday's four-year anniversary of the Iraq invasion.

"Too many people have died and it doesn't solve anything," said Ann Bonner, who drove to Washington through snow with her family from Ohio. "I feel bad carrying out my daily activities while people are suffering, Americans and Iraqis."

Australian Prime Minister John Howard, meanwhile, declined to commit to a timeline for withdrawing the country's 1,400 troops from Iraq.

"Great progress has been achieved, but there is still work to be done," Howard said during a news conference with al-Maliki. "As you know, I don't set speculative dates. There is nothing to be achieved by that."

Howard, a staunch U.S. ally, arrived in Baghdad after his plane was forced to make an emergency landing in southeastern Iraq because it filled with smoke, according to the Australian Associated Press. No one was injured.

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