A suicide bomber detonated explosives at a mosque in western Baghdad killing at least 18 people, security and medical officials said.
The blast in the Harthiyah area, which also wounded at least 30 people, is the latest in a string of bombings in the Iraqi capital that have killed dozens of people in recent days.
There was no immediate claim for the attack, but suicide bombings are almost exclusively carried out by jihadists in Iraq, including members of the Islamic State (IS) group, which has seized large areas of Iraq since June.
