A suicide blast claimed by the Islamic State group (IS) at a Shiite mosque in Islamabad killed at least 31 people on Friday, with 169 more wounded in the deadliest attack in Pakistan’s capital since the 2008 Marriott hotel bombing.

City officials said 31 people died in the explosion at the Imam Bargah Qasr-e-Khadijatul Kubra mosque in the Tarlai area on the city’s outskirts, with scores more being treated for injuries. The death toll was expected to rise further.

The blast occurred at Friday prayers, when mosques around the country are packed with worshippers. “The attacker was stopped at the gate and detonated himself,” a security source said.