At least 15 people were killed and over 30 injured when a suicide bomber blew himself up amidst scores of worshippers attending Friday prayers at a Shia madrassa on the outskirts of city in Pakistan’s restive northwest, officials said.

About 200 men had gathered for the weekly prayers at the Madrassa Hussainia in Gulshan Colony of Peshawar, the capital of Khyber-Pakhtunkhwa province, when it was targeted by the bomber.

The bomber and two accomplices shot and seriously injured a police guard before entering the madrassa from its rear.

The worshippers were listening to a sermon by the prayer leader when the bomber entered the hall and detonated his explosive vest.

Superintendent of Police Shafiullah Khan said that at least 15 people were killed. Other officials said more than 30 people, including several children, were injured. At least four injured men were in a serious condition, they said.

Footage on television showed the walls and ceiling of the seminary were pitted by ball bearings packed into the bomber’s explosive vest. The building’s windows and doors were blown out.

The bomber’s accomplices escaped after the blast. Security forces cordoned off the area and launched a search operation but were unable to trace them. No group claimed responsibility for the attack.

President Asif Ali Zardari and Prime Minister Nawaz Sharif strongly condemned the attack on the madrassa.

In a message, Zardari said such cowardly and heinous acts by militants “cannot weaken the nation’s resolve to pursue its struggle against militancy and the fight against this scourge would continue till its logical conclusion”.