Iraqi soldiers opened fire Friday on Sunni anti-government protesters demanding the Shiite prime minister step down, health officials said.At least four people were killed and 42 wounded, according to provincial health officials, in the shootings in Falluja in the western Anbar province, a Sunni stronghold where protesters have been denouncing what they call second-class treatment by the government.
The officials backed off earlier reports that at least five people were killed, citing the chaos of scene.
The shooting began, according to witnesses, after Iraqi soldiers ordered demonstrators to stop filming security force positions. Protesters, in turn, responded by throwing tear gas and non-lethal explosive devices known as flashbangs, witnesses said.
Still other witnesses told CNN that the soldiers began shooting after they were pelted with objects thrown by protesters.
The incident inflamed protesters, who chanted: "Those are al-Maliki's forces, those are al-Maliki's militias," referring to Prime Minister Nuri al-Maliki.
Religious leaders in Falluja have called for Iraqi forces to leave the city. They also called for a funeral procession Saturday for those killed in the incident.
"We have been demonstrating peacefully. But now we warn al-Maliki that the blood of Falluja martyrs will not be shed in vain" protester Abdul Wahed Ammar said.
The minister of defense, meanwhile, ordered an investigation into the shootings, according to Anbar Satellite TV. Iraq's government spokesman did not immediately respond to a CNN request for comment.
The protest in Falluja, dubbed "Friday of No Retreat" by organizers, is the latest in a series held in predominantly Sunni regions of Iraq. They have been countered by mostly Shiite, pro-government demonstrations, raising fears that the sectarian division could translate to violence in the streets.
The protests have grown in recent weeks. They began in late December when Sunni demonstrators took to the streets in Anbar province, which borders on Jordan and Syria, to protest al-Maliki's order to arrest the bodyguards of Finance Minister Rafaie Esawi, a Sunni.
The arrest of Esawi's bodyguards came just hours after President Jalal Talabani, a Kurd who is widely viewed as a stabilizing political force in Iraq, left the country to undergo treatment for cancer.
The protesters also are demanding the release of detainees they said were held without charges, calling the government corrupt and accusing it of unfairly targeting Iraq's Sunni people.
Iraq's Arab Sunnis and Kurds have accused al-Maliki and his Shiite political party of working to consolidate power in Iraq by cutting them out of the political process, an allegation that comes as U.S. lawmakers raise concerns about Iraq strengthening its ties with Shiite-dominated Iran.
Sunnis make up about 20 percent of Iraq's estimated population of more than 27 million, whereas about 60 percent to 65 percent are Shiite.
Since the fall of Saddam Hussein's Sunni-dominated regime in 2003, Sunnis in Iraq have been largely disaffected. The gulf was widened in 2005 when Sunnis boycotted the country's election, opening the way to a heavily dominated Shiite government.
The sectarian divisions translated into violence in the streets in 2006 and 2007, with fighting that nearly ripped the country apart.
CNN's Chelsea J. Carter contributed to this report.