Ugandan opposition leader Kizza Besigye has urged his supporters to exercise restraint after two of his supporters were shot dead on Wednesday.
Dr Besigye's campaign has been hit by frequent court appearances
President Yoweri Museveni's main rival in next week's elections said the violence was part of a military campaign to intimidate his supporters.
Uganda's police chief has apologised but also partly blamed opposition supporters for the incident.
Two men believed to be state security agents are being held by police.
In an interview with the BBC's Will Ross in Kampala, Dr Besigye called on his supporters "to use maximum restraint" and "to only do what is necessary to defend themselves".
Military police were deployed after Wednesday's shooting
The opposition leader has asked his supporters "not to retaliate" and "not to escalate the violence".
However, Dr Besigye believes that the authorities have been trying to frighten the country's voters ahead of next week's poll.
Wednesday shooting is "consistent with the terror campaign aimed at causing despondency within the population so that the population resigns and says we better keep Museveni or we get finished", he said.
Police say a state security agent fired after a crowd of opposition supporters attacked his car. The man was later arrested together with the driver of the car.
The incident happened in Kampala after supporters were celebrating the adjournment of Dr Besigye's treason trial until after next week's presidential poll.
Dr Besigye's 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 the charges against him are politically motivated.
Compared to elections five years ago, the electoral campaigns have been relatively peaceful.
But our correspondent says Wednesday's shooting is likely to raise tension in an election which has been bitterly fought.
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.