A suicide bomber blew himself up inside a tent filled with mourners in a predominantly Sunni district of Baghdad on Sunday, killing at least 16 people, police and medical sources said.
A further 35 people were wounded in the attack in Doura, which came a day after a triple bombing at a funeral in Baghdad's Shi'ite stronghold of Sadr City killed 85 people.
Iraq's delicate sectarian balance has been strained to near breaking point by the civil war in neighboring Syria, where mainly Sunni Muslim rebels are fighting to overthrow a leader backed by Shi'ite Iran.
Both Sunnis and Shi'ites have crossed into Syria from Iraq to fight on opposite sides of the conflict.
Al Qaeda's Iraqi and Syrian branches merged this year to form the Islamic State of Iraq and the Levant, which has claimed responsibility for attacks on both sides of the border.
Iraq has also witnessed several incidents in recent weeks suggesting that Shi'ite militias, which have so far largely refrained from retaliating for attacks by Sunni insurgents, may once again be resorting to violence.
Around 800 Iraqis were killed in acts of violence in August, according to the United Nations.
"Violence in all forms must be condemned, but I am particularly appalled by the increasing number of vicious attacks against those already bereaved," the acting U.N. envoy to Iraq, Gyorgy Busztin, said in a statement.
"Retaliation can only bring more violence and it is the responsibility of all leaders to take strong action not to let violence escalate further".