Three explosions at a high school in western Kabul killed at least six people and injured a number of students, Afghan security and health officials said.
Many residents in the neighbourhood belong to the Shia Hazara community, an ethnic and religious minority frequently targeted by Sunni militant groups, including Islamic State.
"Three blasts have taken place...in a high school, there are some casualties to our Shia people," said Khalid Zadran, the spokesman for Kabul's commander.
He said later that six people had been killed and 11 injured in the explosions.
The head of a hospital nursing department, who declined to be named, said at least four people had been killed and 14 wounded in the blasts.
Another medical centre, Emergency Hospital, said it had received one dead body and 10 teenagers injured in the explosions.
There was no immediate claim of responsibility for the attack, which followed a lull in violence over the cold winter months and after foreign forces withdrew last year.
Afghanistan's Taliban rulers say they have secured the country since taking power in August but international officials and analysts say the risk of a resurgence in militancy remains and the Islamic State militant group has claimed several attacks.
An official familiar with the matter who declined to be named said the explosive devices had been hidden in backpacks and one had detonated inside the school gates.
Humanitarian group Save the Children's Afghanistan Country Director Chris Nyamandi condemned the blast.
"Save the Children is outraged and strongly condemns the reported attack on a high school today in Kabul. We're deeply saddened about reports that children have been injured, and possibly killed, in the blasts," he said in a statement.
Successive administrations have failed to curb deadly attacks on the Hazara minority in western Kabul including at mosques, a maternity ward and schools in recent years. Last May a huge blast outside a girls' high school in the area killed at least 80 people, most of them female students.