MOSUL, Iraq — A suicide bomber killed at least 21 people at the funeral of a member of Iraq’s Shabak ethnic minority near the northern city of Mosul 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 Shiite, 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 Shiite Iran.

“I was attending the funeral sitting with the women when we heard a huge explosion,” said Umm Mohammed, who was at the funeral in Bartella, about 15 miles east of Mosul in Nineveh Province. “When we went out, we found some men either killed or injured.”