KABUL, Afghanistan — The Islamic State group has claimed responsibility for a suicide bombing on a peaceful protest in the Afghan capital Saturday that killed 81 people and wounded 231, marking the first time the extremists have struck Kabul and raising fears of their growing strength and capability in Afghanistan.

The attack was the deadliest to hit Kabul in 15 years of civil war. It struck a demonstration by Afghanistan's Hazara ethnic community, who were marching for a regional power line to be routed through their home province. The Hazaras are Shiite Muslims; most Afghans are Sunnis.

Footage on Afghan TV and photos posted on social media showed a scene of horror and carnage. Bloodied survivors were seen being dragged from the area, while others walked around dazed or screaming.

Two suicide bombers had attempted to target the march, but one was shot by police before he could detonate his explosives, said Haroon Chakhansuri, a spokesman for Afghan President Ashraf Ghani.

Chakhansuri said three city district police chiefs were injured and another three security personnel killed.

Witnesses said that after the blast, security forces shot in the air to disperse the crowd. Secondary attacks have been known to target people who come to the aid of those wounded in a first explosion.

Roadblocks that had been set up overnight to prevent the marchers accessing the city center or the presidential palace hampered efforts to transfer some of the wounded to the hospital, witnesses said.

Demonstrators sealed some of the area and prevented police and other security forces from entering. Some threw stones at security forces.

The Interior Ministry's deputy spokesman, Najib Danish, said the blast was the biggest in Afghanistan since 2001, when the Taliban launched their brutal insurgency after they were toppled by the 2001 U.S. invasion.

Chakhansuri said organizers of the march had been warned of the possibility of an attack.

“We had intelligence over recent days and it was shared with the demonstration organizers, we shared our concerns because we knew that terrorists wanted to bring sectarianism to our community,” he said.

Senior Hazara leaders were absent despite having attended a similar protest in May. The organizers could not be contacted for comment on Chakhansuri's allegations.

The Islamic State group, also known as ISIS, claimed responsibility for the attack in a statement issued by its news agency, Aamaq.

ISIS has had a presence on Afghanistan's eastern border with Pakistan, mainly in Nangarhar province, for the past year. Ghani has announced a military offensive in Nangarhar, expected to start within days, aimed at eliminating ISIS from the country.