Afghanistan is observing a day of national mourning after suicide bombers killed 80 people and wounded 230 in an attack on marchers in Kbual.
So-called Islamic State (IS), the Sunni Muslim militant group, has said it was behind Saturday's attack on members of the Shia Muslim Hazara minority.
The UN mission in Afghanistan has described the attack as a "war crime".
Tadamichi Yamamoto, head of the UN assistance mission, said the attackers had specifically targeted a large number of civilians.
On Saturday, the IS-linked Amaq news agency said two fighters had detonated explosive belts at a "gathering of Shia" in Deh Mazang square.
Correspondents say the statement suggests an intention to foment sectarian strife.
Thousands of members of the Hazara minority were protesting over a new power line, saying its route bypasses provinces where many of them live.
The Taliban, Afghanistan's most prominent Islamist militant group, condemned the attack.
IS has a presence in eastern Afghanistan but this is the first time it has admitted carrying out attacks in the capital.
An Afghan intelligence source told the BBC an IS commander named Abo Ali had sent three jihadists from the Achen district of Nangarhar province to carry out the Kabul attack.
Only one attacker successfully detonated his explosives, the interior ministry said. The belt of the second failed to explode and the third attacker was killed by security forces, the source said.
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