The health of detained veteran Ugandan opposition figure Kizza Besigye has "reached a critical and deteriorating state", his party says, after he was taken overnight to a medical facility in the capital, Kampala.

The 69-year-old politician was driven to a private medical facility under "heavy security", the People's Front for Freedom (PFF) party said, without specifying what he is suffering from.

However, prison authorities denied that Besigye's health was dire, describing his overnight visit to a doctor as a "general check-up".

Besigye, a former personal doctor to President Yoweri Museveni and one of his longest-standing political rivals, has been in detention since November 2024.

The PFF leader was charged in a military court with treason, which carries the death sentence, as well as illegal possession of a firearm and threatening national security. He denies the accusations.

Besigye, who has run for president against Museveni four times, has been in detention with his associate Obeid Lutale since they were both dramatically seized in Kenya and taken back to Uganda.

Last month, a court denied them bail for the fourth time, saying it was too early to release them as they had not yet entered their pleas.

In a statement on Tuesday, the PFF accused Ugandan authorities of denying Besigye proper medical care, noting that his continued detention amounted to a violation of his basic rights.

"It is a tragedy that a man who has dedicated his life to the health and freedom of others is being denied his own right to medical dignity," the PFF said, adding: "We hold the regime and the prison authorities fully accountable for his well-being."

Frank Baine, a spokesman for Uganda's prisons, denied that Besigye's health was critical, saying the opposition figure was under standard medical supervision.

"Kizza Besigye receives necessary treatment like other prisoners and he is fine," Baine said, adding: "This morning he was doing his exercises."

But the PFF described Baine's remarks as a "blatant attempt to mask the physical toll" of Besigye's continued detention, insisting: "Our leader is seriously unwell."

It demanded that Besigye's personal doctors and family be granted immediate and unrestricted access to him, so they can provide specialised and independent medical care.

Speaking to a local TV station, Besigye's wife, Winnie Byanyima, said that her husband had complained of acute stomach pain, a high temperature and he was severely dehydrated.

"He was shaking and unable to walk. He is seriously ill and he refused to be treated by the prison authorities," Byanyima, who is a respected human rights advocate and head of UNAids, added.

Another opposition leader, Bobi Wine, has expressed concern over Besigye's health while in detention, saying his condition appears to be deteriorating amid limited access to medical care.

"We stand fully in solidarity with him and pray for his recovery," Wine said in a post on X.

This is not the first time the veteran opposition leader has been taken ill at Luzira Prison, a maximum security jail in Kampala, where he has been held.

Last February, Besigye was also reported critically ill after he went on hunger strike demanding justice.

Besigye, who last contested the presidency in 2016, has previously accused the authorities of political persecution.

In recent years he has been less active in politics and did not contest the general election earlier this month.

There have been increasing calls by his family, opposition and human rights groups for him to be released on medical grounds.

President Museveni has blamed Besigye and his legal team for the delays in the trial, which he said had resulted in the PFF's leader's continued detention.

Museveni, who has held power since 1986, was on Saturday declared the winner of last week's presidential election with 72% of the vote.

His closest challenger Wine, whose real name is Robert Kyagulanyi, got 25%.

Wine rejected the results as "fake" and has gone into hiding citing threats against his life.