Ugandan opposition figure Kizza Besigye is "critically ill" in jail three days after starting a hunger strike to protest his detention, one of his lawyers told AFP on Thursday.
Besigye, 68, is a leading opponent of the country's President Yoweri Museveni, whom he has challenged unsuccessfully in four elections.
He was abducted in Kenya in November and has been facing the death penalty on treason charges in a court martial that his wife, UNAIDS executive director Winnie Byanyima, has called a "sham".
"We visited him in the prison yesterday but his medical condition is worrying. He is critically ill and needs urgent medical attention," lawyer Erias Lukwago said on Thursday.
Lukwago had earlier announced that Besigye was on hunger strike to protest his "illegal detention" and was too ill to attend court hearings.
"He is unable to move out of his prison cell," he said.
He added that the jail was ill-equipped to treat him and "he should be treated outside the prison if he is to survive".
Prison spokesman Frank Baine declined to comment on Besigye's condition but told AFP: "Our medical facilities are equipped to handle Besigye's health just like it does with other prisoners."
He branded Besigye's lawyers "alarmists" and vowed: "We shall manage his condition as long as he is under our mandate."
Besigye has been awaiting a military trial since November, despite a court ruling last month that it was unconstitutional for civilians to be tried in such a court.
In addition to the treason allegation, Besigye is separately accused of inciting violence when he led a protest against high commodity prices in 2022.
Museveni rejected last month's Supreme Court ruling on trying civilians in military courts.
An army spokesperson had earlier said that "under no circumstances will Colonel Kizza Besigye be released until he faces the full extent of martial law".
The UN and several rights organisations have voiced their concern about the suppression of the political opposition in Uganda in the run-up to the 2026 presidential elections.
Amnesty International called in a statement on Thursday for Besigye's release, saying his detention was illegal and unconstitutional.
The human rights group's regional director for East and Southern Africa, Tigere Chagutah, branded it a "travesty of justice".