At least 17 people have been killed and 26 injured after a bomb blast hit a religious school in northern Afghanistan.

The blast took place in the city of Aybak in Samangan province, reportedly as people were leaving prayers.

The majority of those killed are believed to be children aged nine to 15, a source in Samangan told the BBC.

No group has claimed responsibility for the attack, and the death toll could increase.

“All of them are children and ordinary people,” one doctor was quoted by AFP as saying.

Interior ministry spokesman Abdul Nafee Takkur said the Taliban’s security forces were investigating the attack, and vowed to “identify the perpetrators and punish them for their actions”.

The former president of the Islamic Republic of Afghanistan, Hamid Karzai, said the explosion was a “crime against humanity” in a tweet, and expressed his sympathy to the families of the victims.

Aybak is a historical city that came to prominence as a trading hub and a centre for Buddhists in the 4th and 5th Centuries. It sits around 200 km (130 miles) north of the capital Kabul.

Afghanistan has been rocked by dozens of blasts since the Taliban seized power last year, mostly claimed by the local offshoot of the Islamic State group, known as Islamic State – Khorasan Province (ISIS-K).

The group is the most extreme of the militant groups in Afghanistan and has targeted religious minorities – such as Hazaras – who the Taliban have pledged to protect. However, Human Rights Watch recently observed that “Taliban authorities have done little to protect these communities from suicide bombings and other unlawful attacks”.

In September, at least 54 people – including 51 girls and young women – were killed after a suicide bomber detonated a bomb in the capital city of Kabul. The attacker had targeted a hall where hundreds of students were sitting a test for university admission.

Taliban leaders later blamed ISIS-K for the attack, though the group itself did not take responsibility.