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.
"Three blasts have taken place...in a high school, there are some casualties," 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 IS 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.
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