The Ugandan government blocked opposition leader Kizza Besigye from flying back into the country from neighbouring Kenya on Wednesday, his party said.

"(Ugandan) state security told Kenya Airways that if Besigye was on board they would not be given landing rights," Anne Mugisha, a leading official in Besigye's party told AFP.

Besigye had been receiving medical treatment in Nairobi after being assaulted by police during a demonstration against rising food and fuel prices in Kampala. A series of such protests last month left at least five people dead.

There was no immediate comment from Kenya Airways.

"We are made to understand that Ugandan authorities threatened not to allow the aircraft to land at Entebbe Airport if he (Besigye) was on board the flight," said a source at Nairobi's Jomo Kenyatta airport, who asked not to be named.

Another official from Besigye's Forum for Democratic Change (FDC) told journalists in Kampala that the party's leader might after all be allowed to fly later in the day.

"Right now I am being advised that he might be coming on the next flight," FDC vice president Salaamu Musumba said.

The incident comes on the eve of the swearing-in ceremony for President Yoweri Museveni, who won re-election after February polls in which Besigye mounted the strongest challenge yet to his 25-year rule.

Besigye, 50, won 37 percent of the vote, while Museveni, 62, took 59 percent according to official election results challenged by the FDC, which claimed widespread fraud.

At Entebbe airport outside Kampala, Besigye's destination, journalists including an AFP reporter were forcibly ejected by airport security and police and driven into Entebbe town.

The Ugandan government said it would hold a press conference about Besigye later Wednesday.

Speaking from his Nairobi hospital on Sunday, Besigye vowed to press on with protests in his country despite the injuries he sustained last month.

He said he would contiue to organise "peaceful demonstrations" to press for government action.

Besigye was first taken to hospital in Kampala at the end of April after Ugandan police smashed the windows of his car and sprayed him with tear gas in an incident caught on camera.

He was then transferred to a Nairobi hospital.