Two roadside bombs killed 30 people outside a mosque in the Iraqi city of Baquba just as Sunni Muslim worshippers were leaving following Friday prayers, police said.
The civil war in neighboring Syria has strained relations between Islam's two main denominations across the region, contributing to a resurgence of sectarian violence in Iraq.
A further 25 people were wounded in the Baquba explosions, which occurred about ten minutes apart in the ethnically and confessionally mixed city, situated around 65 km (40 miles) northeast of the capital Baghdad.
The second explosion tore through a crowd of people who had rushed to help those hurt in the first blast.
"We were evacuating the wounded after the first roadside bomb exploded inside a dustbin. Ten minutes later another bomb exploded about six meters away from the first and I got some shrapnel in my stomach," teacher Khalid Jameel, 25, told Reuters from his hospital bed.
It was not immediately clear who carried out the attack.
Separately on Friday a car bomb killed three Shi'ite Muslim pilgrims from Iran in the city of Samarra, where the bombing of a shrine in 2006 touched off the worst sectarian carnage to engulf Iraq after the U.S.-led invasion that toppled Saddam Hussein, a Sunni Muslim.
Violence abated from its peak in 2006-07, but in recent months Sunni Islamist insurgents, who view Shi'ites as non-believers, have been regaining momentum, raising fears of a return to full-blown civil strife in Iraq.
About 800 Iraqis were killed in August, according to the United Nations. That is still well below its height, when the monthly death toll sometimes topped 3,000.