Ugandan police arrested a retired general planning to stand for president on suspicion he sought support from neighbouring Rwanda to remove President Yoweri Museveni.
Henry Tumukunde, a former Museveni ally and ex-security minister, was detained last week.
Police said in a statement he was held on charges of treason, accusing him of enlisting “the support of a neighbouring country to support him in removing the current leadership” – an apparent reference to Rwanda.
Appearing on NBS television on March 4 Tumukunde said: “If I was Rwanda I would wish to support people who want change in Uganda.”
Relations between Uganda and Rwanda have been strained for more than a year over accusations each supports the other’s dissidents.
Uganda is due to hold a presidential election early next year.
Museveni, in power since 1986, is one of Africa’s longest ruling leaders. Government critics and rights campaigners accuse him of using tactics including intimidation by security forces to maintain his grip on power.
A committee of the ruling National Resistance Movement (NRM) endorsed him for re-election.
One of his opponents will be Bobi Wine, a pop star and lawmaker whose large support base among youth fuels worry in the ruling party and provoked a security crackdown on his supporters.
His rallies have frequently been dispersed by security forces using teargas, beatings and arrests.
In the statement, the police accused Tumukunde of inciting violence and hatred.
“His utterances in radio and television interviews seek to foster hatred that might lead to inter-community violence,” it said.
Tumukunde said if elected, he would speed up Uganda’s preparations to pump its crude oil reserves.
Production of the reserves, discovered 14 years ago, has been repeatedly delayed by disagreements with international oil firms and slow progress in the construction of infrastructure including an export pipeline.