A suicide bomber detonated explosives inside a tent where local Shiite tribal leaders were meeting in northern Baghdad on Wednesday, killing at least 15 people, officials said.
The blast in the Sadr City area also wounded at least 34 others, the officials said.
There was no immediate claim of responsibility but suicide bombings are a tactic almost exclusively employed by Sunni militants in Iraq, who consider members of the Shiite majority apostates and frequently attack them.
The blast comes as Sunni jihadists push south in a lightning offensive that has seen them take control of all of one province and significant parts of two others in two days.
Violence in Iraq is running at its highest level since 2006-2007, the height of a bloody Sunni-Shiite conflict in which tens of thousands were killed.