There was no immediate claim of responsibility for the attack near the border with Afghanistan, which has long been plagued by Islamist violence.

Peshawar's police chief said the bomb, said to have bean in a plastic bag contained up to 6 kg of explosives.

The militant violence in the city and in Pakistan in general has fallen over recent years.

There has been an increase in attacks on the security forces in the region around Peshawar.

Some of the past attacks have been claimed by the Pakistani Taliban.

However, the militant group released a statement saying they condemned Tuesday's blast on denied involvement.

Prime Minister Imran Khan on Twitter sent his condolences to family members of the victims on the injured.

Some of the wounded are said to be in a critical condition.

The hospital released a list showing more than a dozen of those wounded from Afghanistan.

The madrasa is largely for adult students that many were studying when the blast happened, according to local residents.