Kenyan riot police have fired tear gas in the capital against protesters demanding constitutional reform.
The protesters defied a police ban on the rally
Police armed with batons and others on horseback chased demonstrators from the edge of Uhuru Park on the outskirts of Nairobi's business district.
The rally was organised by the main opposition party and a faction of the governing coalition.
Politicians and legislators joined hundreds of students and demonstrators as they took to the streets.
The Red Cross said at least 16 people had been injured during the clashes between police and protesters.
Last Monday President Mwai Kibaki said the 30 June deadline for having a new constitution would be missed.
The constitution has deeply divided the ruling Narc coalition and led to a government shake-up this week.
"Kenyans do not fall asleep, the struggle is still on," chanted the protesters, who had defied a police ban on the public rally.
The ban was imposed because the rally clashed with another political meeting and there were fears of violence.
After coming to power in December 2002, President Kibaki promised to introduce a new constitution within 100 days, but the deadline was put back to 30 June this year, before being again postponed.
Elected president appoints PM
PM appoints cabinet
PM leads government and chairs cabinet
President remains head of armed forces
The Liberal Democratic Party's (LDP) Raila Odinga had been promised the new powerful post of prime minister in return for backing Mr Kibaki in the election.
A constitution review body earlier this year recommended the creation of a prime minister and the reduction of the president's powers despite opposition from Mr Kibaki's allies.
Mr Kibaki said political divisions along ethnic lines had hampered progress with the constitutional review, but that he remained committed to having a new constitution.
On Wednesday, Mr Kibaki brought members of the former ruling Kanu party into government and demoted LDP members.