Winnie Byanyima, wife of Ugandan opposition leader Kizza Besigye, has called on the Ugandan government to release her husband, whom she claims was abducted in Nairobi.

Byanyima said Besigye, leader of Uganda's Forum for Democratic Change (FDC) party, was kidnapped in Nairobi while attending the launch of Narc Kenya leader Martha Karua's book on Saturday.

"I am now reliably informed that he is in a military jail in Kampala," she said on Wednesday.

Besigye's family and lawyers are demanding access to him.

"He is not a soldier. Why is he being held in a military jail?" Byanyima asked rhetorically.

Besigye's disappearance comes in the wake of the arrest of thirtly-six Ugandan activists in Kisumu in July.

Kisumu Governor Anyang Nyong'o said Kenyan agencies mounted the operation in support of their Ugandan counterparts.

The activists, associated with the FDC leader, were abducted and taken back to Uganda, where they were charged with treason and remanded at Kitalya Prison.

A Ugandan court recently released them on bail after they pleaded not guilty to the charges, stating they had been attending a workshop at the time of their arrest.

They also decried torture during detention.

Museveni critic

Besigye has contested and lost four presidential elections against incumbent Yoweri Museveni, who has been in power since 1986.

Once Museveni's personal doctor, Besigye later became one of his most vocal critics, often referring to the president as a "dictator."

He has repeatedly alleged electoral fraud in previous presidential elections, a claim the government denies.

Ugandan police have arrested the opposition figure on numerous times in the past.

On one occasion, police shot him in the hand, and on another, he suffered eye injuries after security agents doused him with pepper spray.

Authorities have accused him of provoking unrest, often charging him with inciting violence.