BBC News, Kampala
Police in Uganda have used tear gas to prevent an opposition political party from staging a rally in the centre of the capital, Kampala.
Police cordoned off Constitution Square and diverted traffic
The Democratic Party was intending to release a report into the assassination almost 20 years ago of a prominent politician and former rebel leader.
The report into Andrew Kayiira's death was never published by the government.
Democratic Party leaders say it names members of the armed forces as being responsible for the murder.
The rally, which was scheduled to take place at midday, never began as police cordoned off the city's Constitution Square and diverted traffic.
The heavy security presence drew the interest of hundreds of people, but even these peaceful crowds were dispersed using tear gas.
The Democratic Party had planned to release a report into the death of one of their former members at the rally.
Dr Andrew Kayiira was a politician who had also been a rebel leader at the same time as President Yoweri Museveni, running a rival group to his National Resistance Movement in the 1980s.
President Museveni later made Dr Kayiira minister for energy, but he was murdered in Kampala in 1987.
At the time the Metropolitan Police investigated his death at the request of the Ugandan government, but their report has never been made public.
A few days ago Uganda's Interior Minister Dr Ruhakana Rugunda was reported as saying that the Ugandan government had never received the report.
But the Democratic Party accuse him of lying. They say they have a copy which names members of the armed forces in 1987 that it says masterminded and carried out the murder.
They now say they will make the report public next Saturday.