Health ministry sources have said as many as 20 people were killed and at least 87 wounded in Saturday's suicide bombing at the funeral of a Senator's son in Khair Khana in Kabul city.

The explosion took place at about 3.30pm during the burial service at a cemetery for Mohammad Salem Ezadyar who was killed on Friday when security forces opened fire on demonstrators at a mass rally in downtown Kabul.

According to sources, three suicide bombers detonated their explosives back-to-back during the ceremony.

High-ranking officials had been in attendance at the time, including CEO Abdullah Abdullah and acting foreign affairs minister Salahuddin Rabbani.

Photographs after the explosion showed Abdullah was safe while Rabbani took to Twitter and confirmed he was unharmed but condemned the incident.

Other high-ranking officials were also in attendance including a number of MPs. Early reports indicated that at least one MP had been wounded.

The wounded have been taken to Kabul Emergency Hospital.

President Ashraf Ghani, who condemned the attack via Twitter, and said the country was under attack.

President Ghani condemns the outrageous attack on mourners burying the martyred.The country is under attack.We must be strong and united, he said.

This comes just hours after two high-ranking security officials warned members of the public against attending mass gatherings. Both the Kabul Garrison Commander and the deputy minister of interior Murad Ali Murad said on television the threat level in Kabul was extremely high, therefore people should avoid public gatherings.

This week has been a particularly deadly week for Kabul after five people were killed during the mass rally in the city on Friday. They had been protesting against Wednesday's massive truck bombing which killed over 100 people and wounded more than 600.

The Taliban immediately denied any involvement in the cemetery bombing.