Unrest elsewhere left three others dead, as authorities grapple with Iraq's worst bloodshed since 2008. The country is stuck in a prolonged political deadlock as Syria's 30-month civil war causes regional instability.
Two roadside bombs went off outside the Al-Salam mosque, a Sunni place of worship in the confessionally mixed city of Baquba, at around midday as Sunnis and Shiites left after a joint prayer session.
Thirty people were killed and 24 wounded in the twin explosions, according to an army major and Ahmed al-Azzawi, a doctor at the city's main hospital.
It remains one of Iraq's least stable areas, and is regularly struck by deadly attacks.
Three car bombs in and around the city killed 10 people on Tuesday.
Attacks also struck elsewhere in Diyala. Another bombing targeted a mosque in the town of Khanaqin, killing one person, and a car bomb at a market north of Baquba wounded five.
In the restive northern province of Nineveh, a shooting and a bombing killed a soldier and a municipal official.
Officials have sought to tackle the violence with high-profile operations targeting militants and tough traffic restrictions in the capital, but attacks continue to rock much of the country.
They have vowed to press on with the campaign, which they say has led to the capture of hundreds of fighters and the killing of dozens more, as well as the dismantling of training camps and bomb-making sites.
