At least 31 people are reported to have been killed and 169 injured.
According to the intelligence group SITE, which monitors extremism online, IS stated that the attack was carried out by a suicide bomber.
"Attacking places of worship and civilians is a heinous crime against humanity and Muslim values. Pakistan stands united against terrorism in all its forms," wrote the country's Deputy Prime Minister Ishaq Dar in a post on X.
The attack is the deadliest in Islamabad since 2008, when 60 people were killed in a bomb attack on a luxury hotel.
