The Islamic State (IS) extremist group has claimed responsibility for a suicide attack in Kabul that has killed over 60 people, one of the deadliest attacks to hit the Afghan capital since the U.S.-led invasion in 2001.
The twin suicide bombings targeted mostly members of the Hazara minority, thousands of whom had gathered to protest a power line on July 23.
The Islamic State group's Amaq news agency reported that two IS fighters detonated explosive belts at the peaceful march, which was attended by an estimated 10,000 people.
Health Ministry spokesman Mohammad Ismail Kawoosi said the blasts left at least 61 dead and 207 wounded.
Kawoosi said many of the injured were in "serious condition" and expected the death toll to rise.
Kabul hospitals were overwhelmed, with reports emerging of blood shortages and urgent appeals for blood donors circulating on social media.
"The horrific attack on a group of peaceful protesters 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 attack, adding that the casualties included security forces.
"Holding protests is the right of every citizen of Afghanistan and the government puts all efforts to provide security for the protesters, 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.
WATCH: Before Bombing, Hazara Protest Over Power Line Route
Afghan Chief Executive Abdullah Abdullah condemned the "terrorist attack."
Gruesome photos circulating on social media showed horrific scenes with scores of people wounded in the square where the protesters had gathered.
Taliban militants denied involvement in the attack. "We want to make it clear," Taliban spokesman Zabihullah Mujahid said in an e-mail to media outlets. "Our mujahedin had no hand in the attack."
The local IS affiliate in Afghanistan is mainly made up of former Taliban fighters disillusioned by the group's failure to overthrow the government despite a 15-year insurgency.
IS has seized pockets of territory in eastern Afghanistan, along the porous border with Pakistan.
The Hazara protesters were demanding that the 500-kilovolt transmission line from Turkmenistan to Kabul be rerouted through the central province of Bamiyan, which has a large Hazara population.
The government says this plan would cost millions and delay the project by years.
Demonstrators gathered near Kabul University, several kilometers from the main government area, waving Afghan flags and chanting slogans such as "Justice! Justice!" and "Death to discrimination!”
The original plan was for the power line to run through the Bamiyan Province, where most of the country’s Hazara live.
The government says the new route, through the Salang Pass north of Kabul, would save millions of dollars in costs and expedite the project.
The Hazara are a Dari-speaking, Shi'ite community that has long been persecuted in Afghanistan.
They are considered the poorest of the ethnic groups and often complain of discrimination.
Only between 30 and 40 percent of Afghans are connected to the electric grid.
Based on reporting by Reuters and AP