A suicide bomber blew himself up at a funeral inside a tent filled with mourners in a predominantly Sunni Muslim district of Baghdad, 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 Shia Muslim stronghold of Sadr City killed at least 85 people.
Iraq's delicate sectarian balance has been strained to near breaking point by the civil war in neighbouring Syria, where mainly Sunni Muslim rebels are fighting to overthrow a leader backed by Iran.
Both Sunni and Shia Muslims 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 Shia militias, which have so far largely refrained from retaliating for attacks by Sunni fighters, may once again be resorting to violence.
The United Nations on Sunday warned against revenge attacks for the Sadr City blasts.
"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 UN 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."
Around 800 Iraqis were killed in acts of violence in August, according to the UN.