A suicide bomber killed at least 21 people at the funeral of a member of Iraq's Shabak minority in the northern province of Nineveh on Saturday, security and medical sources said.
It was not immediately clear who was behind the attack, but Sunni Islamist militants have in the past targeted Shabaks, who are predominantly Shi'ite, warning them to leave the area.
Iraq's delicate sectarian balance has come under acute strain from the war in neighboring Syria, which has pitted mainly Sunni rebels against a leader backed by Shi'ite Iran.
"I was attending the funeral sitting with the women when we heard a huge explosion," said Umm Mohammed, who at the funeral in Bartella, 25 km (15 miles) east of Nineveh's capital, Mosul.
"When we went out, we found some men either killed or injured," she said.
Sunni Islamist insurgents, who view Shi'ites as non-believers, have been regaining momentum in Iraq in recent months, raising fears of a return to the scale of intercommunal violence that peaked in 2006-07 following the U.S.-led invasion.
About 800 Iraqis were killed in acts of violence in August, according to the United Nations. That is still well below its height, when the monthly death toll sometimes topped 3,000.