A suicide bomber wearing an explosive vest blew himself up among mourners inside a funeral tent on a farm about 12 miles north of Baghdad, Iraq, on Monday, according to police.
At least 21 people were killed and 35 others injured at the funeral in al Taji, a mostly Sunni district, officials said.
The funeral was for a member of the local Awakening Council, a group also known as the Sons of Iraq and Sahawat, made up of Sunni Arab fighters who turned against al Qaeda.
Iraqi security forces believe that ISIS militants were behind the attack.
Awakening Councils are U.S.-backed groups that have been active in Iraq since 2006. A few years ago, the councils were credited as being a major factor in a drop in violence across Iraq, but council members have also become targets for jihadists.