The Afghan Interior Ministry says the death toll in the Kabul bombing has risen to 80.
At least 231 people were wounded after two suicide bombers targeted a peaceful demonstration in Kabul's Dehmazang Square on Saturday.
Two attackers detonated their suicide vests, while "one was killed by Afghan security forces," said the ministry statement.
Earlier, the Health Ministry said 64 people had been killed and 265 were wounded.
The Islamic State extremist group claimed responsibility for the attack.
Update 14:55 - Islamic State has claimed responsibility for the attack
At least 61 people were killed and 207 wounded when twin explosions hit a large demonstration in Kabul, an Afghan official says.
"We expect the numbers to rise unfortunately," Health Ministry spokesman Ismail Kawusi added.
Islamic State has claimed responsibility for the attack, writing on the group-affiliated Aamaq News Agency that two of their fighters detonated explosive belts at the demonstration, which took place in the Dehmazang area of Kabul.
The protest was being held in connection to CASA-1000, a project to build a 1,222-kilometre power transmission line to transport electricity from Kyrgyzstan and Tajikistan through the country to Pakistan and India.
Much of the city center had been sealed off with stacks of shipping containers and other obstacles as the march began earlier on Saturday, and security was tight with helicopters patrolling overhead.
The casualties include Afghan security forces providing security for the protest, according to an email from the Afghan presidential palace.
Update 14:10 - Taliban rejects hand in Kabul attack
The Taliban militants group has rejected hand in a deadly attack targeting the demonstration in Kabul city which left more than 200 people dead or wounded.
The Taliban group spokesman Zabiullah Mujahid said the group has no link with the explosions in Kabul city, calling it a grim move to create divisions among the people.
Mujahid further added that the group condemns any move that lead to creation of divisions, including ethnic and religious divisions among the people of Afghanistan.
Without elaborating further Mujahid said the attack was carried out by the enemies.
Protests will continue
Within an hour of the attack, angry demonstrators started regrouping in the Dehmazang Circle area. Many said they would stay on the streets until their demands are met.
One demonstrator said the protests will continue until the legitimate voice of the people is heard.
This comes after government overnight blocked most access points into the city center in a bid to prevent demonstrators from reaching the presidential palace.
In depth coverage
At least 61 people have been killed and 207 wounded when two suicide bombers detonated explosives at a large demonstration in Kabul on Saturday afternoon, Health Ministry spokesman Ismail Kawusi said.
A heavy explosion in Kabul targeting protesters has left scores of casualties, an official said.