Iraqi officials say an explosion inside a Sunni mosque has killed at least 15 people in a city north of Baghdad.
A city official in Samarra says the blast during Friday prayers also wounded at least 15.
Violence between Sunnis and Shiite Muslims in Iraq has risen sharply in recent months. The attacks have raised fears of all-out sectarian warfare.
Earlier this week, car bombs ripped through Baghdad - part of a series of explosions across Iraq that left at least 31 dead.
The violence escalated after the pullout of U.S. troops in 2011.