KABUL — A suicide bomber struck a Shiite mosque in the Afghan capital Monday, killing 32 people, the U.N. office said, the second large-scale attack targeting minority Shiites in Kabul in just over a month.

Hours later, the Islamic State affiliate in Afghanistan claimed responsibility for the attack, according to the SITE Intelligence Group, a U.S. monitoring service that tracks militant postings.

Afghan police said the bomber, who was on foot, walked into the Shiite mosque in western Kabul where he detonated his explosives among a crowd of worshipers.

The U.N. Assistance Mission in Afghanistan said the explosion also wounded more than 50 people, many of them children.

In its statement, Islamic State said the group’s martyr hit a gathering of close to 1,000 inside a “temple of Shiite polytheists” in Kabul and detonated his vest bearing 35 pounds of explosives, SITE said. Islamic State claimed nearly 200 Shiites were killed and wounded. However, militants often exaggerate their claims.

Sunni extremists such as the Taliban and Islamic State view Shiites as heretics and apostates and frequently target Shiite mosques and public gatherings.

Monday’s bombing hit during a prayer ceremony commemorating 40 days since the anniversary of the death of Imam Hussein, the slain grandson of the prophet Muhammad. The ceremony is known as Arbaeen, meaning “forty” in Arabic. Hussein is a revered Shiite martyr who was killed in A.D. 680 in the city of Karbala in present-day Iraq.

In early October, militants attacked another Shiite ceremony at a shrine in Kabul, commemorating the anniversary of Hussein’s actual death. That attack killed 17 people, mostly worshipers but also several police officers. A day later, a similar attack struck Shiites in the city of Mazer-e Sharif in northern Balkh province, killing at least 14 people.

The Islamic State affiliate in Afghanistan also claimed responsibility for one of those two attacks, the U.N. statement said.

Faredoon Obiadi, head of the criminal investigation department for the Kabul police, said the attacker in Monday’s bombing walked into the Baqir-ul Ulom mosque and mingled among the crowd on the first floor of the two-story building where he detonated his explosives.

“Suddenly, a huge explosion happened, then everything went dark,” said Ewaz Ali, 50, who was inside the mosque but suffered only minor wounds.

Shiites in Afghanistan make up an estimated 15 percent of the country’s population of around 30 million. Their public celebrations and commemorations were largely banned during the five years when the Taliban controlled the country.