Dr Waheed Majroeh, the head of international relations for the Ministry of Public Health, said 207 people were also wounded by the blast, which was claimed by the Islamic State group.
The bombing struck a group of ethnic Hazara demonstrators who had been marching through Kabul.
A statement reported by the IS-Linked Aamaq online news agency said two IS militants detonated their explosive vests amid the crowds of minority ethnic Hazara demonstrators.
Hazaras are predominantly Shiite Muslims, and IS views all Shiites as apostates. Shortly before the IS statement, the Taliban’s spokesman denied any Taliban involvement in the blast.
The Taliban have been waging a vicious insurgency against the Kabul government for 15 years, since their regime was overthrown by the US invasion in 2001.
The marchers were demanding that a major regional electric power line be routed through their impoverished home province. Most Hazaras are Shiite Muslims but most Afghans are Sunni.
Eyewitness Ramin Anwari described seeing up to eight bodies in the Demazang area, where protesters were preparing to set up a camp after a four-hour march.
EmoticonEmoticon