Kampala (AFP) - At least 30 people, including serving soldiers and an opposition MP, have been detained on suspicion of plotting to overthrow Uganda's government, the army said on Friday.

"We and the police are investigating the matter," army spokesman Colonel Paddy Ankunda told AFP, saying the group was suspected of planning an armed uprising against President Yoweri Museveni, himself a former rebel who seized power 30 years ago.

Ankunda said the detainees were "linked to a rebel group" that he declined to name.

He said most of those arrested were soldiers, adding that at least one lawmaker and another opposition politician had been arrested.

The only detainee named by the spokesman was Michael Kabaziguruka, an MP from the main opposition Forum for Democratic Change (FDC) party whose leader Kizza Besigye is in custody on treason charges.

Besigye, who cried foul after coming second to Museveni in February's presidential election, was arrested last month for holding a mock swearing-in ceremony.

He was previously charged with treason in 2005 but the case was eventually abandoned. At the time, prosecutors accused him of leading a shadowy rebel group named the People's Redemption Army, a charge Besigye always denied.

Party spokesman Ssemujju Nganda went to visit Kabaziguruka after his arrest.

"He told me he was questioned on rebel links, which he didn't know about," said Nganda, adding that other party supporters "are under detention on the same claim".

A long-standing opponent of Museveni, Besigye has been frequently jailed, placed under house arrest, accused of both treason and rape, tear-gassed, beaten and hospitalised over the years.

Local newspaper the Daily Monitor said one of the arrested soldiers is a captain responsible for the armoury at Bombo Military Barracks, the army headquarters north of the capital Kampala.

It also quoted the FDC spokesman as saying that Kabaziguruka had been grilled "about Dr Besigye and General (David) Sejusa's links to the same rebel group".

Sejusa was Uganda's former spymaster.