Boniface Kariuki on life support after successful surgery, KNH surgeons say

 When police officers Masinde Barasa and Duncan Kiprono assaulted hawker Boniface Kariuki in Nairobi's CBD. [Screen Grab]

Boniface Kariuki, a trader who was shot by police during clashes with protesters on Tuesday, is on life support, surgeons who operated on him have said.

Violent clashes erupted in Nairobi on Tuesday after protesters demanding an end to police brutality were attacked by a large gang of motorbike-riding "goons" and police officers.

The clashes added to tensions in Kenya, already on edge as it marks a year since massive protests over the economy.

Anger has focused on the incident in which an unarmed man who was selling face masks was shot point-blank in the head by a police officer.

The shooting, seen by AFP reporters and filmed by bystanders, led to protesters calling for new marches on Thursday.

William Sigilai, the acting head of Kenyatta Hospital, said the victim "was critically ill with a gunshot wound to the head, resulting in severe brain injury and excessive bleeding".

The bullet was removed in surgery and he was transferred to the intensive care unit where "he remains on mechanical ventilation".

"While his condition is still critical, he is alive and under close, round-the-clock observation and care by our medical team," Sigilai said in a statement.

Kenyatta Hospital received 16 patients related to the protests, with injuries ranging from gunshot wounds to blunt trauma.

Nine were discharged after treatment, but seven others required surgery, the hospital said, without giving further details.

The protests had been called over alleged police brutality after Albert Ojwang's death in custody this month.

Amnesty International, as part of a coalition of rights groups in Kenya, condemned the actions of police officers, saying their "responsibility to protect was completely abdicated".