Twenty-two people were killed and 55 wounded in clashes in Baghdad, police said today, the worst eruption of violence in the capital since Shi'ite cleric Moqtada al-Sadr called his fighters off the streets a week ago.
The violence in Sadr's Baghdad stronghold, the Shi'ite slum of Sadr City, follows a week of relative calm after a crackdown by Prime Minister Nuri al-Maliki on Sadr's followers led to battles across the south and Baghdad late last month.
In a reminder of instability further north, a group of roughly 40 students were kidnapped by gunmen for several hours near the city of Mosul before Iraqi security forces freed them.
The unrest comes only days before US ambassador Ryan Crocker and US commander General David Petraeus are due to deliver key testimony to the US Congress on progress in Iraq.
Gunfire could be heard throughout the day in Sadr City, the stronghold of Sadr's Mehdi Army and home to 2 million people in eastern Baghdad.
US Apache helicopter gunships swooped overhead and a column of black smoke towered over the Jamila market, a vast bazaar on the edge of the slum that supplies foodstuffs for much of the eastern half of capital.
"I have lost my cousin in these clashes today. I think Maliki will be happy now," a Mehdi Army street commander who gave his name as Abu Ammar said.
Police said a joint operation by the US military and Iraqi forces had started in the early hours of Sunday and fighting had reached the outskirts of densely populated Sadr City.