Namibia said on Friday that it had declined a visa extension to a Ugandan king visiting for medical treatment after rumours he had been abducted sparked protests that put at risk Namibian diplomatic staff abroad.

Bugandan King Ronald Muwenda Mutebi II was granted a 90-day visa upon arrival in April on a private medical visit, the Ministry of Home Affairs said.

But some of his supporters alleged that the Namibian and Ugandan governments had conspired to abduct him, it said.

The unscrupulous Subjects organised demonstrations at Namibian embassies abroad to demand Mutebis release, the ministry said.

This did not only put at risk the security of Namibias personnel abroad but interfered greatly with the operations and security of Namibias diplomatic missions, it said, without specifying in which countries the protests took place.

Namibia said it had engaged with the Buganda royal family and Ugandan government but the disruptive activities continued unabated.

Ugandan media reported that five Buganda clan leaders were briefly detained after travelling to Namibia to check on their king earlier this month.

This reportedly prompted a rebuke from President Yoweri Museveni, who requested all Ugandans to stop embarrassing the country.

Windhoek said it was eventually pushed to decline a renewal when Mutebis visa expired. The monarchs medical team, his palace and Ugandan authorities were thoroughly briefed.

It was not immediately clear whether Mutebi, 69, who was receiving treatment for an undisclosed ailment, had already left the country.

The Baganda make up the largest ethnic grouping in Uganda and their kingdom was granted considerable autonomy after independence from Britain in 1962.

However independence leader Milton Obote outlawed tribal kingdoms and forced the king into exile. The bush war that brought Museveni to power in 1986 was successful largely due to support from Buganda.

Mutebi occupies a largely ceremonial role but has previously had run-ins with Museveni, who has ruled over Uganda with an iron fist. (AFP)