Doug Stanglin

USA TODAY

At least 80 people were killed and 231 injured Saturday when suicide bombers attacked a large demonstration in the Afghan capital of Kabul, according to the Afghan Interior Ministry.

The demonstration was organized by ethnic Hazaras demanding that a major regional power line be rerouted through their impoverished home province. Most Hazaras are Shiite Muslims but most Afghans are Sunni.

The Islamic State, also known as ISIS or ISIL, claimed responsibility for the attack, saying in a statement on its Amaq News Agency that two of its fighters detonated explosive belts during the march.

Presidential spokesman Haroon Chakhansuri told the Associated Press that one of the suicide bombers was shot by the police. He said that three city district police chiefs on duty at the square were injured and another three security personnel were killed.

If the Islamic State claim is confirmed, it would mark the first time the terror organization mounted an attack in the Afghan capital.

President Ashraf Ghani condemned the blast and declared Sunday a day of national mourning. “Peaceful demonstrations are the right of every citizen of Afghanistan and the government will do everything it can to provide them with security,” Ghani said in a statement.

Footage on Afghan television and photographs posted on social media showed a scene of carnage, with numerous bodies and body parts spread across the square. Angry demonstrations sealed some of the area around the square and prevented police and other security forces from entering. Some threw stones at security forces.

The U.S. State Department issued a statement saying it "condemns in the strongest terms" the "vicious attack."

"The killers responsible for this bloodshed do not represent the future for Afghanistan and will not prevail," the statement said. "Attacks like these only strengthen our resolve to continue our mission in Afghanistan and deepen our support for the people and government there."

Amnesty International issued a statement saying the “horrific attack” on the Hazara rally “demonstrates the utter disregard that armed groups have for human life.”

“Such attacks are a reminder that the conflict in Afghanistan is not winding down, as some believe, but escalating, with consequences for the human rights situation in the country that should alarm us all,” it quoted Champa Patel, Amnesty’s South Asia director, as saying.

Violence had been feared at what was the second demonstration by Hazaras over the power line issue. The last one in May attracted tens of thousands of people and shut down the central business district.

The May march was attended by Hazara political leaders, who were notable by their absence Saturday. At the height of the march, demonstrators chanted slogans against Ghani and Chief Executive Abdullah Abdullah, shouting “death to discrimination” and “all Afghans are equal.”

The so-called TUTAP line is backed by the Asian Development Bank with involvement of Turkmenistan, Uzbekistan, Tajikistan, Afghanistan and Pakistan. The original plan routed the line through Bamiyan province, in the central highlands, where most of the country’s Hazaras live, according to the AP.

The previous Afghan government changed the route in 2013. Protest leaders have said that the rerouting was evidence of bias against the Hazara community, which accounts for up to 15% of Afghanistan’s estimated 30 million people.

They are considered the poorest of the country’s ethnic groups, and often complain of discrimination. Bamiyan is poverty-stricken, though it is largely peaceful and has potential as a tourist destination.

Fewer than 40% of the Afghan people are connected to the national grid, according to the World Bank. Almost 75% of electricity is imported.