Four anti-government protesters were killed and 19 wounded when the Iraqi army opened fire on Friday, apparently to disperse demonstrators, in a mostly Sunni town west of Baghdad, officials said.
The deaths were the first at the hands of the security forces since massive protests began in mainly Sunni Arab areas of Iraq more than a month ago, railing against alleged targeting of their minority by the Shiite-led authorities.
The demonstration in Fallujah, 60 kilometers west of Baghdad, was one of several that began after Friday prayers across the country.
Protesters had been moving to an area in east Fallujah but were blocked off by soldiers, an army captain said. They began throwing bottles of water at the troops who then opened fire.
A doctor at Fallujah's main hospital confirmed the toll.
It was not immediately clear whether the soldiers fired directly into the crowd, or into the air.
Similar demonstrations, meanwhile, took place in the nearby city of Ramadi, like Fallujah a mostly Sunni town in the western province of Anbar, as well as the cities of Samarra, Mosul and Baquba, all north of Baghdad.
Rallies also took place in Sunni neighborhoods of the capital.
The longest-running of the protests, in Ramadi, has cut off a key trade route linking Baghdad to Jordan and Syria for a month.
"The government should respond immediately to the demands of protesters, before we start a revolution and put an end to it [the government]," said Hassan al-Zaidi, a tribal chief who was protesting in Baquba.
In Baquba, capital of restive Diyala province, protesters carried Iraqi flags called for the "fall of the regime", and held up banners that read, "Iran out, Baghdad always free", a reference to persistent claims by Sunnis that the Shiite-led government is controlled by Shiite neighbor Iran.
Rallies also called for freeing prisoners who demonstrators allege are being wrongfully held, with one banner in Mosul reading, "Enough talk—break the doors of the prisons.”
The protests, all of which have taken place in Sunni majority areas, have hardened opposition against Shiite Prime Minister Nuri al-Maliki and come amid a political crisis less than three months ahead of key provincial elections.
Demonstrators began by criticising the alleged exploitation of anti-terror laws to detain Sunnis wrongfully, but have since moved on to calling for Maliki to quit.
They were sparked by the December 20 arrest of at least nine of the guards of Finance Minister Rafa al-Essawi, a top Sunni politician.
The government has sought to curb the rallies by claiming to have released nearly 900 prisoners in recent weeks, with a senior minister publicly apologizing for holding detainees without charge.