Ugandan opposition leader Kizza Besigye has been admitted to an intensive care unit (ICU) in the capital, Kampala, after collapsing unconscious in court during his treason trial, his wife has said.

The 70 year old has been in detention since November 2024. His lead lawyer was arrested last month and charged with allegedly failing to report acts of treason.

The visibly frail politician was objecting to state lawyers being appointed to represent him when he collapsed, prompting prison guards to rush him to hospital.

"He is unconscious, unable to speak, and unresponsive even to a pain stimulus," his wife, Winnie Byanyima, who heads the UN's agency tackling HIV and Aids (UNAids), wrote on X.

Besigye, who has run for president against long-serving leader Yoweri Museveni four times, was dramatically abducted in Kenya in 2024 and taken back to Uganda.

He has since been held along with his aide, Obeid Lutale, and both have been charged with treason, which they deny.

Prosecutors allege that Besigye and his co-accused plotted to overthrow President Museveni's government.

Treason is a capital offence in Uganda and if found guilty the veteran politician could be sentenced to death.

During Wednesday's hearing at the High Court in Kampala witnesses in court said Besigye repeatedly shouted "stop" about his legal representation before collapsing.

"Before he collapsed, he cried out that he was being injured," his wife posted, adding that Besigye's sister Olive Kobusingye, who is a doctor, was in court but was not allowed to attend to him.

He was transferred to Mulago National Referral Hospital, Uganda's largest public hospital, but was refusing treatment from government medical personnel.

"He will not allow any government official to touch him," Byanyima said.

His wife demanded that Besigye be allowed to receive treatment from his personal physician at a private clinic rather than at a government health facility.

The ICU wing where Besigye is being treated is guarded by heavily armed security officers. Reports say his sister, who is also his personal doctor, has now been allowed to see him.

Besigye's main lawyer, Erias Lukwago, is in jail after being seized by the army last month.

His other lead lawyer, Kenyan Martha Karua, was barred from entering the country when she flew in to represent him last month.

Besigye's son, Adam Ampa, has appealed to President Museveni and his son, Gen Muhoozi Kainerugaba, who is Uganda's army chief, to show mercy by releasing his father on humanitarian grounds.

"Regardless of politics, no son should have to witness his father reach such a state while standing before the very law he served and dedicated his life," Ampa wrote in an open letter shared on social media on Wednesday.

Bobi Wine, a Ugandan opposition politician who fled the country fearing for his life after ​contesting the January presidential election, said Besigye's appearance in court while clearly unwell was a "shocking violation of his most basic rights".

Besigye once served as Museveni's personal doctor before breaking ranks with him in 1999.

He has been less active in politics in recent years, and did not contest the 2021 election.