Another 147 people were wounded in the attack in front of the Sayed Al-Shuhada school, said Danish Hedayat, head of media for the second vice president of Afghanistan.
A car bomb was detonated in the neighborhood of Dasht-e-Barchi, and two more bombs exploded when students rushed out in panic.
There has been no official claim of responsibility yet. The Taliban has denied being behind Saturday evening’s blasts.
But the foreign troop withdrawal has led to a surge in fighting between Afghan security forces and Taliban insurgents. Critics of the decision say the Islamist militants will make a grab for power and civilians live in fear of being subjected once more to brutal and oppressive Taliban rule.
Some of the girls ‘could not be found’
The area where the blasts happened is home to a large community of Shiites from the Hazara ethnic minority, which has been targeted in the past by Islamic State, a Sunni militant group.
Officials said most of those killed were schoolgirls. Some families were still searching hospitals for their children on Sunday.
“The first blast was powerful and happened so close to the children that some of them could not be found,” an Afghan official, requesting anonymity, told Reuters.
On Sunday, civilians and policemen collected books and school bags strewn across a blood-stained road now busy with shoppers ahead of celebrations for Eid al-Fitr next week.
Bodies were still being collected from morgues as the first burials were conducted in the west of the city. Some families were still gathering Sunday outside hospitals to read names posted on the walls, and checking morgues.
“The entire night we carried bodies of young girls and boys to a graveyard and prayed for everyone wounded in the attack,” said Mohammed Reza Ali, who has been helping families of the victims at a private hospital. “Why not just kill all of us to put an end to this war?” he added.
Nekbakht, 18, was one of the pupils killed while studying at the school on Saturday. Her brother Mukhtar, 20, told CNN that the family lives close to the school and came rushing out when they heard a loud explosion — only to see another blast.
On Sunday the family buried Nekbakht near their house. “It was a tough day,” Mukhtar said. “We are fed up with this situation. Every day we face terrible incidents — especially we Hazara people.”
Another schoolgirl, 12-year-old Zahara, was also injured in her arm and head in the attack.
Her uncle, Sadeq Baqhere, who lives a few hundred meters from the school, told CNN she was admitted to hospital for surgery and returned on Monday.
Baqhere described hospitals overwhelmed with hundreds of injured and dozens of killed patients. He said the family “totally blames the government” for not providing security for its people.
“Our enemies are stronger than before,” he said, adding that the situation would continue to deteriorate as foreign forces left the country.
Mukhtar believes the situation will get worse as US troops exit Afghanistan.
“We want everyone to enroll their children in schools, and show them that they cannot prevent us from education,” he said of the perpetrators.
Security was intensified across Kabul after the attack, but authorities said they would not be able to provide protection to all schools, mosques and other public places.
Afghan President Ashraf Ghani on Saturday blamed Taliban insurgents, but a spokesman for the group denied involvement and condemned any attacks on civilians.
Pope Francis called the attack an “inhuman act” in remarks to pilgrims in St. Peter’s Square in Vatican City on Sunday.
United Nations Secretary-General Antonio Guterres also condemned the attack and expressed his deepest sympathies to the victims’ families and to the Afghan government and people.
On Sunday, the Taliban announced a three-day ceasefire through Eid al-Fitr, the Muslim holiday observed at the end of Ramadan.
World powers weigh in
The United States condemned what it described as the “barbarous attack” at the school and called for an “immediate end to violence and the senseless targeting of innocent civilians.”
“We will continue to support and partner with the people of Afghanistan, who are determined to see to it that the gains of the past two decades aren’t erased,” the statement from the US State Department said.
On Twitter, China’s ambassador to Afghanistan, Wang Yu, said the abrupt US announcement of a complete withdrawal of forces had led to a succession of attacks throughout the country.
“China calls on foreign troops in Afghanistan to take into full account the security of people in the country and the region, pull out in a responsible manner and avoid inflicting more turmoil and suffering on the Afghan people,” he said.
Condemning the killing of civilians, India’s foreign ministry said the bombing represented an attack on the future of Afghanistan.
“The perpetrators clearly seek to destroy the painstaking and hard-won achievements that the Afghans have put in place over the last two decades,” a statement said.
Additional reporting by Reuters.