BAGHDAD — The U.N. warned on Sunday against retaliatory attacks in Iraq after two blasts killed 73 people in a Shiite area of Baghdad, a day after a Sunni mosque bombing.

Saturday's bombings struck near funeral tents for a deceased tribal sheikh in the Sadr City area of north Baghdad and also wounded more than 200 people.

It was just the latest attack in a surge in violence that authorities have so far failed to stem — the worst to hit Iraq since 2008, when the country 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 U.N. 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 blasts were not the first targeting mourners in recent months.

The blasts came just a day after two bombs exploded at a Sunni mosque near Samarra, north of Baghdad, killing 18 people.

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.

On Sunday, the bare metal frames of the funeral tents stood at the site of the deadly Sadr City explosions.

Mangled cars sat nearby, and debris including broken dishes and scattered bottles of water distributed to mourners lay on 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, and the worst since April 23, when 95 people died in violence.

The unrest continued on Sunday, with two police killed and seven people, among them six police, wounded in attacks in Nineveh province in Iraq's north.

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.