On Wednesday, a US patrol was hit by a roadside bomb in the centre of Baghdad, killing one American soldier and wounding five others,the US military said.
Two Iraqi civilians also died in the attack near the Green Zone, the police said.
A "penetrator" bomb, which US military officials say are being given to Shiia fighters by Iran, was said to have been used in the attack.
Another US soldier was killed and four wounded in Diyala province, northeast of Baghdad, in a bomb blast, US officials said.
Also on Wednesday, the west Baghdad headquarters of the most influential Sunni clerical group in Iraq was siezed by the authorities, who accused the group of supporting al-Qaeda.
The Association of Muslim Scholars has long opposed the US military presence in Iraq.
The group led calls for the boycott of elections in January 2005.