The UN warned on Sunday against revenge attacks in Iraq after two blasts killed 73 people in a Shiite area of Baghdad a day after a Sunni mosque was bombed.
Saturday'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.
"Violence in all forms must be condemned, but I am particularly appalled by the increasing number of vicious attacks against those already bereaved," he said.
The Sadr City bombings were not the first targeting mourners in recent months.
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.
"Attacks like these are perpetrated by a small minority of terrorists who wish to destabilise Iraq," the British embassy said of the Sadr City blasts.
It called on "all political, religious and community leaders to unite against those who perpetrate these crimes."
On Sunday, 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.
Eighteen more people died in other violence on Saturday, including 11 security forces members, and four people shot dead at a Baghdad alcohol shop.
It was the United Nations' International Day of Peace, which calls for a "complete global cessation of hostilities for one day."
Saturday was the second-deadliest day for Iraq this year, topped only by April 23, when 95 people died in violence.
The unrest continued on Sunday, with two police killed and seven people wounded in attacks in Nineveh province in Iraq's north.
And in the northern city of Kirkuk, a suicide bomber blew up a vehicle near the home of a Christian MP, wounding 47 people, including three of the lawmaker's children.
With the latest violence, more than 570 people have been killed this month and over 4,400 since the beginning of the year, according to AFP figures based on security and medical sources.