At least one soldier was killed and seven other people were wounded when gunmen attacked the regional police headquarters in northern Uganda to try to free an inmate, police said on Monday.
Ugandan police chief Kale Kayihura identified the man as Oola Dan Odiya, who is being held on charges of murder and terrorism related to an attack at a local police post on May 27.
Scores of people have been arrested in the four months since veteran leader President Yoweri Museveni was declared winner of a presidential election on Feb. 18, the opposition says, and protesters have frequently clashed with police.
Kayihura said the attack in Gulu, the biggest town in northern Uganda, happened at about 8 p.m. (1700 GMT) on Sunday, when gunmen drove up in a pick-up firing their guns and tried to storm the station "to free and cause escape of one suspect".
Six security personnel and one civilian were injured in the attack, police said. Eight guns and ammunition were recovered after the attackers dropped their weapons as they fled.
As well as the arrests of its supporters, the opposition says some of its leaders have also been arrested and then released after questioning.
Kizza Besigye, the main opposition leader, was arrested in May and shortly after charged with treason, a charge the opposition says is trumped up.
An opposition legislator was recently arrested and security officials were quoted in local media as saying he was being investigated on suspicions of plotting a coup.
Military spokesman Paddy Ankunda told Reuters about 30 soldiers, including a colonel, had also been arrested in the last few days and were under investigation for various offences.
He did not give any details of those offences but local media has reported they were being questioned over a coup plot.