A blast hit a Shiite Muslim mosque in Pakistan's capital, Islamabad, during Friday prayers.

At least 31 people were killed in the explosion and 169 were injured, police said.

The explosion occurred at the Imambargah Khadijah al-Kubra in the Tarlai area on the outskirts of the capital.

Hospitals in the city were put on high alert in order to take in the numerous wounded.

Pakistani daily Dawn cited Islamabad police spokesperson Taqi Jawad as saying that while the cause of the blast had not yet been established, there were indications that it was the product of a suicide bombing.

The "Islamic State" said one of its militants had targeted the congregation, detonating an explosive vest and "inflicting a large number of deaths and injuries," according to the SITE Intelligence Group, which monitors jihadi communications.

AFP news agency cited an unnamed security source as saying that a suicide bomber was behind the attack.

Reuters cited anonymous police sources as saying that the attacker was stopped at the gate of the mosque before detonating the bomb.

Leaders offer condolences

Prime Minister Shehbaz Sharif expressed his "deep grief" over the incident in a statement, saying that he "strongly condemns" the blast.

President Asif Ali Zardari issued his condolences to the victims' loved ones in a post on social media.

"Targeting innocent civilians is a crime against humanity,"  he said, according to the post issued by his PPP party.

UN Secretary-General ‍Antonio ⁠Guterres meanwhile condemned the suspected attack "in ‌the strongest terms," a spokesperson said.

Germany's ambassador to Pakistan Ina Lepel also offered her condolences.

"We mourn the loss of life in today's horrible attack at Imambargah in Islamabad," she said on social media.

"We hope that those responsible will be found and brought to justice."

Attacks on Shiites in Pakistan

A majority of Pakistanis are Sunni Muslims, while some 15% belong to the Shiite minority.

Islamist groups such as the Pakistani Taliban (TTP) and the "Islamic State" group have carried out attacks on Shiites in the past, with many Sunni extremists considering them to be apostates. 

Pakistan has been grappling with a major security crisis for years, battling armed Islamist groups as well as Baloch separatists in the country's southwest.

The Friday explosion comes after a dozen people were killed in a suicide attack outside an Islamabad district court in November.

UPDATE: This article was updated to reflect that the "Islamic State" claimed responsibility for the explosion.

Edited by: Wesley Dockery