Two bombs near a Sunni mosque north of Baghdad killed 38 people and wounded 55 on Friday, police and a doctor said, after two days of attacks targeting Iraqi Shiites in which dozens died.
One bomb exploded as worshippers were departing the Saria mosque in the city of Baquba while a second detonated after people gathered at the scene of the first blast, the sources said.
The violence raises the spectre of tit-for-tat killings common during the height of sectarian violence in Iraq that killed tens of thousands of people, and comes at a time of festering sectarian tensions between Iraq's Sunni minority and Shiite majority.
The bombings are the latest in a series of attacks that have targeted both Sunni and Shiite places of worship in past weeks, and follow two days of attacks targeting Iraqi Shiites.
On Thursday, a suicide bomber killed 12 people at the entrance of Al-Zahraa Husseiniyah, a Shiite place of worship in the city of Kirkuk, where relatives of victims from violence the day before were receiving condolences.
Car bombs also hit three Shiite-majority areas of Baghdad on Thursday, killing 10 people, while 21 people died in a series of bombings that mainly hit Shiite areas of the capital the day before.
Gunmen also shot dead the brother of a Sunni MP in Baghdad on Thursday.
Violence in Iraq has fallen from its peak, but attacks are still common, killing more than 200 people in each of the first four months of this year, including more than 460 in April, according to AFP figures.