Two people have died after gun shots were fired into a crowd of Ugandan opposition leader Kizza Besigye's supporters in the capital, Kampala.
Dr Besigye's campaign has been hit by frequent court appearances
Police say a state security agent fired after the crowd attacked his car.
It happened after Dr Besigye's treason trial was adjourned until after next week's presidential poll.
Dr Besigye is the main rival to President Yoweri Museveni, but his election campaign has been frequently interrupted by court appearances.
He is accused by the state of plotting a rebellion to overthrow the government, but he says he charges against him are politically motivated.
Six people were also injured in the shooting as the crowds gathered near the centre of the city to welcome Dr Besigye who was at a meeting.
The campaign has been relatively peaceful
The BBC's Will Ross in Kampala says it is not clear why the armed security agent was among opposition supporters, but his presence appears to have provoked them. Afterwards, anti-riot police deployed to the area calm the crowds.
Compared to elections five years ago, these campaigns have been relatively peaceful.
However, our correspondent says news of this shooting is likely to raise tension in an election which has been bitterly fought.
Earlier, the High Court ruled that Dr Besigye's treason trial will begin on 15 March - after the defence challenged the state's case against him.
He has also been on trial accused of rape and been before a military court accused of terrorism.
The adjournment is likely to suit the opposition politician, who is now free to campaign ahead of the 23 February poll.
President Museveni, who came to power 20 years ago, is viewed as the favourite to win.
These are the first multiparty elections for 26 years, but have been marred by the controversy surrounding the arrest of President Museveni's rival.
Last year, Mr Museveni spoke of the need for reconciliation in Uganda, a country which has suffered from decades of conflict.
The election campaign has nevertheless been bitterly fought.
A live television debate is due later on Wednesday, but President Museveni will not be appearing.