At least 400 people were injured, including police officers, according to media reports. The official death toll has not been confirmed, with estimates ranging from eight to 16.

The demonstrations marked the anniversary of last year's anti-tax protests, when 60 people were reportedly killed and dozens abducted by police.

This year, anger intensified following the death of blogger Albert Ojwan, 31, who died in police custody earlier this month.

The demonstrators reportedly targeted government and police offices, chanted for the occupation of the presidential residence and attacked, looted and burned shops and businesses in Nairobi.

At a press conference, Kenyan Interior Minister Kipchumba Murkomen accused protestors of attempting to unconstitutionally enact "regime change."

He also said nine police stations were attacked, dozens of vehicles destroyed, and five guns were stolen.

UN Human Rights response

On Thursday, as smoke still rose from torched buildings in Nairobi, the UN human rights office, OHCHR, released a statement expressing concern.

Alarmed by reports that protesters had been wounded or killed by gunfire, OHCHR stressed that under international human rights law, law enforcement should only use lethal force when strictly necessary to protect life or prevent serious injury from an imminent threat.

The office welcomed the announcement that Kenya's Independent Policing Oversight Authority will investigate the incidents and underlined the need for "prompt, thorough, independent and transparent investigations to bring those responsible to justice" and prevent recurrence.

OHCHR also called for calm and restraint.

UN Spokesperson Stéphane Dujarric echoed these concerns at the daily press briefing in New York, saying: "We are obviously concerned about the violence we have seen in Kenya. We are closely monitoring the situation. We are very saddened by the loss of life."

He also reiterated concerns over the reported gunshot wounds and welcomed plans for oversight investigations.