- Blast hit a demonstration by Hazara minority
- Protest march was over demand of a multimillion dollar power line
- Kabul Police is working to confirm initial reports of the blast
The bombings, apparently aimed at sowing sectarian discord in a country well known for Shia-Sunni harmony, came as thousands of Hazaras gathered to protest over a multi-million-dollar power line.
Charred bodies and dismembered limbs littered the scene of the attack, with ambulances struggling to reach the site as authorities had overnight blocked key intersections with stacked shipping containers to control movement of the protesters.
"As a result of the attack 80 people were martyred and 231 others were wounded," the interior ministry said in a statement.
"Based on initial information, the attack was carried out by three suicide bombers... The third attacker was gunned down by security forces."
The wounded overwhelmed city hospitals, officials said, with reports emerging of blood shortages and urgent appeals for donors circulating on social media.
The Taliban, who are in the middle of their annual summer offensive and are more powerful than ISIS, strongly denied any involvement in the attack.
ISIS claimed the bombings in a statement carried by its affiliated Amaq news agency, calling it an attack on Shiites.
"Two fighters of the Islamic State detonated their explosive belts in a gathering of Shiites in... Kabul," Amaq said.
The attack represents a major escalation for the ISIS group, which so has largely been confined to the eastern province of Nangarhar.
The National Directorate of Security, Afghanistan's main intelligence agency, said the attack was masterminded by Abu Ali, an ISIS commander in Nangarhar's volatile Achin district.
The attack came as thousands of demonstrators gathered to demand that a multi-million-dollar power line pass through their electricity-starved province of Bamiyan, one of the most deprived areas of Afghanistan with a large Hazara population.
"The horrific attack on a group of peaceful protestors in Kabul demonstrates the utter disregard that armed groups have for human life," Amnesty International said in a statement.
"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."
In a statement, Afghan President Ashraf Ghani said he was "deeply saddened" by the carnage, adding that the casualties included security officials.
"Holding protests is the right of every citizen of Afghanistan... but terrorists entered the protests, and carried out explosions that martyred and wounded a number of citizens including members of security forces," the presidential palace said.
The protest march was largely peaceful before the explosions struck as the demonstrators sought to march on the presidential palace, waving flags and chanting slogans such as "death to discrimination".
The 500-kilovolt TUTAP power line, which would connect the Central Asian nations of Turkmenistan, Uzbekistan and Tajikistan with electricity-hungry Afghanistan and Pakistan, was originally set to pass through the central province.
But the government re-routed it through the mountainous Salang pass north of Kabul, saying the shorter route would speed up the project and save millions of dollars.
Hazara leaders in the ethnically divided nation lashed out at the Pashtun president, calling the decision prejudiced against the Hazaras, a community that has suffered a long history of oppression.
The three million-strong Hazara community has been persecuted for decades, with thousands killed in the late 1990s by Al-Qaeda and the mainly Pashtun Sunni Taliban.
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