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At least seven people have died and more than 50 injured after an explosion during a class at a religious school in Pakistan, police have said.

Hospital officials say those killed in the attack, which took place in the northern city of Peshawar, were aged between 20 and 30.

Dozens of others were injured, including four under the age of 13.

No group has yet claimed responsibility. An investigation has been launched.

Earlier reports suggested four of the dead were children, but this has since been retracted.

The city of Peshawar, close to the Afghan border, has seen some of the worst of the violence during the Taliban insurgency in recent years.

Six years ago, gunmen stormed a military school in the city leaving more than 150 dead, including many children.

However, the number of attacks has greatly reduced in recent years.