Kenya has admitted to assisting in the kidnapping of a Ugandan opposition leader on its soil last year, prompting his lawyer to accuse Nairobi of acting like a "rogue state."

Kizza Besigye, 68, who appeared in court for the latest hearing of his treason trial on Wednesday, was abducted by armed men in the heart of the Kenyan capital in November and re-emerged a few days later at a military court in Uganda.

Kenya's government had previously denied any involvement in his abduction.

But in a TV interview late on Tuesday, Foreign Affairs Cabinet Secretary Musalia Mudavadi admitted: "Kenya cooperated with the Ugandan authorities."

'Completely outside of law'

That admission saw Kenyan presidential candidate Martha Karua, who is representing Besigye in his treason trial, declare herself "completely scandalised" by Mudavadi’s admission.

"Kenya is admitting to being a rogue state," said Karua, who described the "arrangements of having Kenya security agencies assist in the abduction and rendition" as "completely outside of the law".

"It's the actions of two rogue states" said Karua.

In explaining his position, Mudavadi told Citizen TV that "(Uganda) is a friendly nation. He (Kizza Besigye) was not seeking asylum. He had not come to say that he was seeking asylum. Had he said that, maybe the treatment would have been different."

Managing relations 'very carefully'

"We have to partner with our East African states and sometimes we have to manage those relations very carefully for the broader national interest," he added.

Karua dismissed Mudavadi's claims of cooperation, saying that it "must be grounded on the rule of law."

Besigye, who appeared for a hearing on Wednesday, was abducted by armed men in the heart of the Kenyan capital Nairobi last November and re-emerged a few days later at a military court in Uganda.

Besigye is a former doctor to President Yoweri Museveni, who has ruled Uganda for nearly 40 years, but turned against him and ran for the presidency on multiple occasions.

Besigye's case moved to civilian court

Rights groups say Besigye's abduction and trial for treason, which carries a potential death penalty, are linked to next January's election, when Museveni, 80, will once again seek re-election.

Besigye's case was moved to a civilian court after he went on hunger strike earlier this year.

But on Tuesday, Ugandan Members of Parliament passed a controversial bill authorising military tribunals for civilians, bypassing a Supreme Court ruling issued in January.

After a brief hearing on Wednesday, Besigye’s case was adjourned to May 29.

'Very disappointing'

One of his lawyers, Erias Lukwago, called it "very disappointing".

"There is a tendency by court to keep adjourning this case and denying them opportunity to get bail," he told AFP.

Activists say the kidnapping and trial are part of a wider erosion of democracy across East Africa.

Tanzanian opposition leader Tundu Lissu is also on trial for treason in his country ahead of elections in October.

Calls for release of Kenyan activist in Tanzania

Several foreign activists who attempted to attend his trial this week were detained and deported – including Karua.

Karua, a former justice minister, accused Kenya, Uganda and Tanzania of "collaborating to oppress the citizens (and) violate their rights."

A Kenyan activist and Ugandan journalist are still missing after being arrested by Tanzanian police.

In a statement, assorted rights groups condemned the "arrest and incommunicado detention" of the two and called for their "immediate and unconditional release."