Suicide bombers attacked Shiite pilgrims in Baghdad and a primary school and police station in a Shiite village in north Iraq on Sunday, killing at least 24 people, officials said.
Violence has reached a level unseen since 2008, amid persistent fears of a relapse into the kind of intense Sunni-Shiite bloodshed that peaked in 2006-2007 and killed tens of thousands of people.
A suicide bomber detonated explosives near pilgrims walking to a shrine in north Baghdad to commemorate the death of Imam Mohammed al-Jawad, the ninth Shiite imam.
The blast killed at least nine people and wounded 30 others, officials said.
A bus parked near the site of the explosion had a streak of blood running from a shattered window down its side.
Pieces of human flesh hung from a roadside tree, and blood was spattered on a pavement and the underside of a bridge.
Two young boys sifted through debris at the site, where items including sandals and a policeman's belt buckle lay in a pool of water formed when emergency personnel hosed the street down.
"We are not afraid of the explosion, we are not afraid of death," said Hussein Haidar, a pilgrim walking to the shrine after the attack.
Even after the blast, security forces performed only cursory searches of people entering the area.
Iraq is home to some of the holiest sites in Shiite Islam, and millions of pilgrims visit them each year.
But crowds of pilgrims are frequently targeted by Sunni militants including those linked to Al-Qaeda, who consider Shiites to be apostates.
Two more suicide bombers on Sunday targeted the Turkmen Shiite village of Qabak in Nineveh province about 50 kilometres (30 miles) from the border with Syria.
10 schoolchildren killed
The bombers detonated explosives-rigged vehicles at a police station and a primary school, killing 15 people and wounding 44, local official Abdulal Abbas told AFP.
Ten children and five police were killed, Abbas said, adding that the school bombing collapsed the building's roof.
Sunday is a normal schoolday in Iraq, where the weekend is on Friday and Saturday.
"Al-Qaeda terrorists... carried out the crime because we are Shiites," a weeping mother whose young son was wounded in Qabak said at a hospital in Dohuk province.
Other attacks on Sunday killed nine people.
A bombing in east Baghdad killed at least five and wounded 14, while two blasts in the northern province of Kirkuk killed a Kurdish security forces member and wounded another.
And a roadside bomb killed three police and wounded one near Ramadi, west of Baghdad.
In Iraq, almost nothing is safe from attack by militants.
They have struck highly secure targets such as prisons, and also bombed cafes, markets, mosques, football fields, weddings and funerals.
Sunday's blasts came a day after violence including an attack on Shiite pilgrims in Baghdad and a suicide bombing at a cafe killed at least 73 people.
Among them were two journalists from the Sharqiya television channel gunned down in the northern city of Mosul.
UN envoy Nickolay Mladenov called on Iraq's "political, religious and civil leaders to work together with the security forces" to curb the bloodshed.
“It is their responsibility to ensure that pilgrims can practise their religious duties, that schoolchildren can attend their classes, that journalists can exercise their professional duties, and that ordinary citizens can live a normal life," Mladenov said in a statement.
A US embassy statement deplored the "abhorrent suicide attack against a primary school.
"This attack targeting innocent school children and the recent attack against pilgrims in Baghdad are reprehensible," it said.
Diplomats and analysts say the Shiite-led government's failure to address the grievances of Iraq's Sunni Arab minority -- which complains of political exclusion and abuses by security forces -- has driven the surge in unrest.
Violence worsened sharply after security forces stormed a Sunni Arab anti-government protest camp in northern Iraq on April 23, sparking clashes in which dozens died.
The authorities have made some concessions aimed at placating anti-government protesters and Sunnis in general, such as freeing prisoners and raising the salaries of Sunni anti-Al-Qaeda fighters, but underlying issues remain unaddressed.
The latest violence takes this month's death toll to more than 160, and more than 4,850 since the beginning of the year, according to AFP figures based on security and medical sources.