The civil war in neighbouring 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 around ten minutes apart in the ethnically-mixed city 40 miles north-east of the capital Baghdad.
The second explosion tore through a crowd of people who had rushed to help those hurt in the first blast.
Speaking from his hospital bed, teacher Khalid Jameel, 25, said: "We were evacuating the wounded after the first roadside bomb exploded inside a dustbin.
"Ten minutes later another bomb exploded about six metres away from the first and I got some shrapnel in my stomach."
It was not immediately clear who carried out the bomb attack.
Separately, a car bomb killed three Shi'ite Muslim pilgrims from Iran in the city of Samarra, where the bombing of a shrine in 2006 sparked off the worst sectarian carnage to engulf Iraq after the US-led invasion that toppled Saddam Hussein.