KABUL — Two explosions rocked a peaceful demonstration in Kabul, the capital of Afghanistan, on Saturday, organizers and eyewitnesses said, with the government reporting at least 80 dead.

The Afghan Interior Ministry, in a statement, reported the casualties and said 231 had been wounded in the blasts.

The Islamic State, in a statement through the group’s Amaq News Agency, claimed the carnage as a “martyrdom attack on Shias.’’ The Taliban, who are often behind major assaults in Afghanistan, denied any involvement.

Afghan security officials said that while Kabul remained under constant insurgent threat, they had no intelligence on a particular threat to the protest.

Much of the city was already under lockdown; the government had stacked shipping containers to block routes to the presidential palace in anticipation of the demonstration by Hazaras, an ethnic minority group. They had gathered in the west of the city to demand that a proposed electricity transmission line be routed through the Hazara-dominated central province of Bamian.

The Hazaras have only in the past decade tried to shake off a long history of oppression. The protest leaders claimed the government remained rife with “systematic bias’’ against the Hazaras and had routed the electricity transmission line elsewhere, depriving the central Afghan region not only of electric power but also of the roads and other infrastructure that would come with it.

The government has rejected the claims, saying the route of the transmission line was decided purely on technical grounds.

Muhammad Ali, a protester at the site of the blast whose clothes were covered in blood, said he had loaded dozens of dead bodies into trucks.

“People were going toward a prayer break when two explosions happened — one near the truck where speeches were given,’’ Ali said.

Hundreds of protesters returned to the site immediately after the carnage, cordoning off the area with a large Afghan flag they had carried in their march earlier, lowering the cordon only to allow ambulances to pass. When the armored vehicle of a government official approached, angry men chased it away.

As tempers flared at the government, protesters also pushed away antiriot police forces who had provided security earlier in the day.

Saturday’s attack was the deadliest of the past 15 years on the Hazaras, a largely Shia group. In December 2011, a suicide-bombing in a Shia shrine in Kabul killed at least 63 people, mostly Hazaras.

Saturday’s attack puts further pressure on President Ashraf Ghani’s struggling government. As it tries to build momentum by introducing reforms, Ghani’s coalition administration has struggled with infighting and meeting deadlines to hold parliamentary elections. The protest over the electricity transmission line has only added to the administration’s woes.