Two bombs hidden inside air conditioners have exploded in a Sunni mosque packed with worshippers killing at least 18 people.
The deputy head of the municipal council in the city of Samarra, where the explosions took place, said the blasts went off around midday, during Friday prayers.
The official, Mizhar Fleih, said at least 21 people were also wounded in the attack.
Fleih said that the Musaab Bin Omair mosque was heavily damaged in the explosions.
"We are worried that the attacks on Sunni and Shia mosques aim at reigniting the sectarian strife in this country," he added.
Samarra is a largely Sunni city that is home to a revered Shia shrine. It is 95km north of Baghdad, the Iraqi capital.
Iraq is weathering its worst bout of violence in half a decade. Deaths have risen significantly since April, with more than 4,000 killed since the start of that month.
Last week, a similar attack on a Sunni mosque northeast of the capital killed 33 worshippers.