A suicide attacker detonated an ambulance packed with explosives in Tikrit on Sunday, killing nine people at the southern entrance to the city, police and hospital sources said.
The bomber struck during the busy morning rush hour. Authorities declared a curfew in the city, saying they had information that further attacks were possible.
In Samarra, about 50 km (30 miles) south of Tikrit, two people were killed when a suicide car bomber struck a car park for Shi’ite pilgrims visiting the city’s al-Askari mosque, sources said.
The attacks took place as Iraqi troops and security forces, backed by a US-led international coalition, were fighting to drive Islamic State militants out of the northern city of Mosul which they have controlled for the last two years.