Twenty people were killed and at least 96 wounded when a suicide bomber targeted worshippers at a mosque in the northwestern city of Peshawar, Pakistan, authorities said Monday.

Saddique Khan, a senior police official in the city, said no one immediately took responsibility for the attack, the Associated Press reported. About 150 people were reportedly praying inside the mosque where the bomber struck.

The news agency said police officers from nearby officers were among the people inside the mosque. The bomber had a suicide vest on and the explosion caused the roof to collapse, injuring many people, police said.