Two Kenyan campaigners against illegal police killings have been murdered by unidentified gunmen.
Oscar Foundation director Kamau Kingara and programmes co-ordinator Paul Oulo were shot after gunmen blocked their car on a central Nairobi street.
Small demonstrations broke out afterwards and a student was shot dead by police in the early hours of Friday. Police said three officers were arrested for using live ammunition against students, who had taken the body of one of the activists.
Students protested again as darkness fell on Friday and police fired tear gas at youths blocking a street and throwing rocks and bottles outside Nairobi University's main campus.
The UN special rapporteur on extrajudicial executions, Philip Alston, who met both rights activists during a visit to Kenya in February, called for a foreign-led investigation into their killings.
"It is imperative, if the Kenyan police are to be exonerated, for an independent team to be called from somewhere like Scotland Yard or the South African police to investigate," Alston said in a statement in New York.
Washington offered the FBI's services to catch the killers.
Gathering protests against alleged extrajudicial police killings have added to widespread disillusionment with the poor record of a year-old coalition government formed to end the east African country's bloody post-election crisis a year ago.
The two Oscar Foundation officials had mobilised protests on Thursday against what they said was the illegal killing of 1,721 young people and the disappearance of 6542 others suspected by the police of being Mungiki members or sympathisers.
Other rights groups and a UN special investigator put the number killed in a crackdown, mainly in 2007, at about 500.
The Mungiki gang, which draws support from Kenya's young and jobless, is known for extortion and gruesome killings, including beheadings. It claims to be the successor of Kenya's anti-colonial Mau Mau rebel movement.