So far, 80 bodies and more than 260 wounded people were taken to hospitals in Kabul, according to Ismail Kawoosi, a spokesman for the Afghan Health Ministry.
The attack, the worst in terms of casualties in months, drew attention to ISIS instead of the Taliban, which had been blamed for recent bombings.
Two ISIS fighters detonated their suicide belts among the protesters, according to ISIS' media wing, Amaq. A third attacker was killed by security forces before detonating his bomb, according to an Afghan security official speaking on condition of anonymity.
The jihadist terrorist group has been stepping up attacks worldwide -- and most recently in Afghanistan -- while losing territory in its self-proclaimed caliphate in Iraq and Syria.
The blast in Kabul on Saturday afternoon happened during a demonstration by members of the Hazara, a Shiite minority group, near the Afghan Parliament building and Kabul University.
The protesters were demanding a planned power line be rerouted through their poverty-stricken Bamyan province to ensure electricity in the relatively isolated area west of Kabul.