At least 23 people were killed when Iraqi security forces stormed a Sunni Muslim protest camp near Kirkuk on Tuesday, triggering a gun battle between troops and protesters and provoking insurgent attacks in other areas.
It was the worst fighting Iraq has seen since thousands of Sunni Muslims started staging protests in December to demand an end to perceived marginalization of their sect by Prime Minister Nuri al-Maliki's Shi'ite-led government.
Iraq's education minister and its science and technology minister, both Sunni Muslims, offered to resign on Tuesday in protest against the raid, according to the deputy prime minister's office and their Iraqiya party.
Hours after violence in Hawija, Sunni Islamist militants fought gun battles with police and army outside Kirkuk and west of the capital Baghdad in Ramadi.
In the first clash, Iraq's defense ministry said troops opened fire early on Tuesday after coming under attack from gunmen in the makeshift protest camp in a public square in Hawija, near Kirkuk, 170 km (100 miles) north of Baghdad.
"When the armed forces started... to enforce the law using units of riot control forces, they were confronted with heavy fire," the defense ministry said in a statement.
The defense ministry and military sources said troops found rocket-propelled grenades, sniper rifles, AK-47 guns and other weapons at the camp.
But protest leaders said they were unarmed when security forces stormed in and started shooting in the morning.
"When special forces raided the square, we were not prepared and we had no weapons. They crushed some of us in their vehicles," said Ahmed Hawija, a student.
The defense ministry said 20 gunmen were killed at the camp along with three of its officers. Three military sources said twenty people at the camp and six soldiers died.
Sectarian tensions still simmer close to the surface in Iraq where intercommunal fighting between Shi'ite militias and Sunni insurgents killed tens of thousands of people at the height of the war that followed the 2003 invasion.
The Hawija clashes will likely widen divisions in Maliki's cross-sectarian government which has been deadlocked by fighting among Shi'ite, Sunni and ethnic Kurdish parties over how to share power since the last American troops left in 2011.
After the Hawija raid, security forces imposed a curfew in the surrounding province of Salahuddin, burned protesters' tents and cleared the square.
Later in the day, Sunni tribal members attacked and briefly seized control of three checkpoints in villages around Hawija before armed forces backed by helicopter gunships took them back, military sources and tribal leaders said.
Gunmen also attacked Iraqi army posts to the south of Kirkuk, wounding four soldiers, and insurgents burned two army humvees on the highway outside Ramadi, 100 km (60 miles) west of Baghdad. Military officials said three soldiers were killed.
Violence in Iraq has eased since the intercommunal slaughter that erupted after al Qaeda militants bombed an important Shi'ite shrine in 2006 and triggered a wave of retaliation by Shi'ite militias on Sunni communities.
But Sunni Islamist militants are still capable of major attacks. Al Qaeda's local wing has stepped up its campaign of bombings and suicide blasts since the start of the year in an attempt to provoke more widespread sectarian confrontation.
Since the last U.S. troops left in 2011, Iraq's government has been mired in crisis over a power-sharing agreement that splits post among the Shi'ite, Sunni and ethnic Kurdish parties. Maliki's critics accuse him of amassing power at their expense.
Many Iraqi Sunnis say they have been sidelined after the U.S.-led 2003 invasion that ousted Sunni strongman Saddam Hussein and allowed the country's Shi'ite majority to gain power through elections.