KABUL, Afghanistan — The Islamic State claimed a bombing that left at least 80 people dead Saturday at a peaceful demonstration in the Afghan capital of Kabul, raising fears that the group may be extending its reach beyond the country’s eastern pockets, where it generally operates.

The Afghan Interior Ministry, in a statement, said the attack on thousands of Hazaras, an ethnic minority group staging the protest, had been a suicide mission.

“The attack was carried out by three suicide bombers: The first person carried out a blast, the second one failed at his detonation, and the third terrorist was killed in shooting by the security forces,” the ministry said.

The second assailant was presumed to be at large, a security official said, speaking on the condition of anonymity as he was not authorized to discuss intelligence matters.