Four US soldiers have been killed by an explosion south of the Iraqi capital, Baghdad, the US military has said.
An overnight strike in Sadr City reportedly killed two civilians
The soldiers were part of a task force to stop the flow of weapons and men to militant groups, it added.
The US military also said it had detained 30 militants with suspected links to al-Qaeda in raids around Iraq.
Meanwhile a joint US-Iraqi operation in the Sadr City area of Baghdad killed two civilians, according to a policeman quoted by Associated Press news agency.
AP said the joint force backed up by helicopters attacked houses in the Shia stronghold overnight.
The agency also said the house of an aide to radical Shia cleric Moqtada Sadr had been raided in the holy city of Kufa, 160km (100 miles) from Baghdad.
The 30 al-Qaeda suspects arrested at the weekend included 17 men detained in Karma near Baghdad, accused of links to car bomb attacks, including some using chlorine gas, the military said.
Other suspects were held in Baghdad, Mosul, Tarmiya, Samarra and Tikrit.
Meanwhile hundreds of mourners turned out in Najaf, another holy city, for the funeral of a governor and a police chief who were assassinated on Saturday.
Diwaniya province governor Khalil Jalil Hamza and police chief Maj-Gen Khaled Hassan were returning from a funeral when a bomb exploded beside their convoy.
The governor was a key figure in the Badr Organisation, the military wing of the largest Shia Muslim party, the Supreme Islamic Iraqi Council.
Security was tight for the funeral in the centre of Najaf.
The US administration has sent about 30,000 extra troops to Iraq since February, as part of a plan to improve security in and around Baghdad.
More than 3,000 American soldiers have died in combat since the US-led invasion of Iraq in March 2003.