Yesterday's bombings struck near funeral tents for a tribal sheikh in the Sadr City district of north Baghdad and also wounded more than 200 people.
It was just the latest in an upsurge of violence that has brought death tolls to their highest level since 2008, when Iraq was emerging from a brutal sectarian conflict.
"Retaliation can only bring more violence and it is the responsibility of all leaders to take strong action not to let violence escalate further," Gyorgy Busztin, the UN secretary general's deputy special representative for Iraq, said in a statement.
The Sadr City bombings were not the first targeting mourners in recent months.
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They came after two bombs exploded on Friday at a Sunni mosque near Samarra, north of Baghdad, killing 18 people.
Militants have carried out a number of attacks on both Sunni and Shiite mosques this year.
Iraq was ravaged by a bloody Sunni-Shiite conflict that peaked in 2006-2007 and killed thousands of people.
There are persistent fears, bolstered by various sectarian attacks this year, that Iraq may return to all-out conflict between the country's Shiite majority and Sunni minority.
It called on "all political, religious and community leaders to unite against those who perpetrate these crimes."
Today, mourners placed coffins containing the bodies of victims of the blasts atop vehicles for transport to Najaf for burial near the shrine of Imam Ali, one of the holiest sites in Shiite Islam, an AFP journalist said.
Bare metal frames were all that remained of the funeral tents in Sadr City. Debris including broken plastic furniture and bottles of water distributed to mourners littered the ground.
It was the United Nations' International Day of Peace, which calls for a "complete global cessation of hostilities for one day.