Police in the Kenyan capital, Nairobi, have fired tear gas to disperse hundreds of opposition supporters who were about to hold a demonstration.
Police said they were not notified of the protest and so it was illegal
Some 500 opposition supporters, including 20 MPs, were protesting about a government decision to recognise a breakaway faction of the Kanu party.
The rally, which was to be held in Uhuru Park, was in support of ousted Kanu leader Uhuru Kenyatta.
The police said they were not notified of the protest and so it was illegal.
Last week's decision by the registrar of societies means Mr Kenyatta, son of Kenya's founding president, Jomo Kenyatta, is no longer the official leader of the opposition.
Instead, Nicholas Biwott, a former key ally of ex-President Daniel arap Moi takes that position.
Kanu split over whether to join a popular opposition political alliance, the Orange Democratic Movement (ODM), which is set to compete in presidential elections due next year.
Kanu was in power for almost 40 years after independence in 1963, until President Mwai Kibaki defeated Uhuru Kenyatta in 2002 elections.
Mr Kibaki replaced Mr Moi, who stood down.
"What has happened today is a travesty of justice and we shall not relent until we, the bonafide officials of Kanu, are recognised," Mr Kenyatta told a press conference in parliament.
"It wants to manipulate and appoint opposition leaders so that there is no criticism from anybody."
But government spokesman Alfred Mutua said the demonstration should never have taken place.
"Internal problems should be sorted out in political party boardrooms and not in the street or through intimidation," Associated Press news agency quoted him as saying.