The bombing targeted a Shia mosque during Friday prayers. At least 31 people were killed and 169 were injured.
A regional branch of the Islamic State group has claimed responsibility for the suicide attack. According to the IS propaganda channel Amaq, the attacker first opened fire on security guards who tried to stop him at the entrance, then detonated the explosive device a short distance inside.
Pakistan's Interior Minister Mohsin Naqvi says the mastermind behind the attack is among those arrested.
The attack is the deadliest in Islamabad since 2008, when around 60 people were killed in a bomb attack on a luxury hotel.
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