Ugandan police arrested a retired general on suspicion that he sought support from neighboring Rwanda to remove President Yoweri Museveni.
Henry Tumukunde, a former ally of Museveni and ex-security minister, was detained on Thursday.
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.
While appearing on NBS television on March 4 Tumukunde said: “If I was Rwanda I would wish to support people who want to cause change in Uganda.”
Relations between Uganda and Rwanda have been strained for more than a year over accusations that they support each other’s dissidents.
Uganda is due to hold its next presidential election early next year.
Tumukunde plans to run.
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) has already endorsed him to stand for re-election.
One of his opponents will be Bobi Wine, a pop star and lawmaker whose large support base among the youth has fuelled 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 also accused Tumukunde of inciting violence and hatred.
“His utterances in a series of radio and television interviews…seek to foster hatred that might lead to inter-community violence,” it said.
Tumukunde has said that if he is elected, he would speed up Uganda’s preparations for the pumping of 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 such as an export pipeline.