Attacks across Iraq on May 21 left at least 20 dead and many more wounded.
In the bloodiest attack, a car bomb exploded near a Sunni mosque in western Baghdad, killing 11 people and wounding 21 more.
The fresh violence comes a day after some 70 people were killed in violence targeting majority Shi'a.
Nearly 300 people have been killed in the last week amid rising sectarian tensions, partly fueled by the conflict in neighboring Syria.
In Washington, White House press secretary Jay Carney said the U.S. administration was "deeply concerned by the frequency and the nature of recent attacks."
He said U.S. officials in Baghdad and Washington were in contact with a wide range of senior Iraqi leaders "to urge calm and help resolve ongoing political and sectarian tensions."
Based on reporting by AP and Reuters