One bomb exploded inside Al-Wardiyah mosque in the city of Hilla, while a suicide bomber detonated an explosives-rigged belt at Al-Graita mosque nearby, the sources said.
Both blasts, which also wounded another 71 people, occurred during evening prayers.
Dozens of Sunni and Shiite mosques have been targets of such attacks in Iraq this year.
In one of the deadliest attacks, two bombs exploded near the Sunni Saria mosque in Baquba, north of Baghdad, after prayers on Friday.
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Those bombings came after a suicide bomber detonated an explosives-rigged belt on Thursday at the entrance to Al-Zahraa husseiniyah, killing 12 people.
Yesterday, Prime Minister Nuri al-Maliki called for joint Shiite-Sunni prayers on Fridays in a major Baghdad mosque.
"Those who target mosques are enemies of Sunnis and Shiites alike, and are planning to ignite (sectarian) strife," he said in a statement and today he said he will overhaul Iraq's security strategy.
Protests broke out in Sunni areas of Iraq almost five months ago.
While the government has made some concessions, freeing prisoners and raising the salaries of Sunni anti-Al-Qaeda fighters, the underlying issues have not been addressed.