Police took away Ugandan opposition politician Robert Kyagulanyi as he got off a plane at the country's main airport on Thursday on his return from abroad, but an official denied that he was under arrest.

Kyagulanyi, a prominent challenger to long-ruling President Yoweri Museveni, had been in the United States to receive treatment for injuries he said were sustained during torture by security forces.

His return has rattled the government headed by the 74-year-old president, who leads a nation where nearly 80 percent of the population is under the age of 30.

Security forces had deployed around Entebbe International Airport and the highway linking it to the capital Kampala ahead of his arrival to prevent supporters from greeting him. Armoured personnel carriers and police vehicles lined the highway.

The Daily Monitor newspaper reported that police arrested him on the tarmac after he disembarked.

But a police official said he was being escorted to his home and was not under arrest.

The official, who was not authorized to speak on the record, told Reuters that Kyagulanyi was "just being taken home". Residents in his neighbourhood told Reuters that they had attempted to wait for him on streets near his home but were chased away by security forces.

Kyagulanyi, a 36-year old pop star and reggae musician turned legislator, is widely seen as posing a significant challenge to Museveni, who has ruled since 1986.

His message - that young Ugandans need a dynamic new head of state to tackle the myriad problems they face - has electrified citizens who say they are fed up with corruption, unemployment, and state repression of dissent.

The government denies allegations of corruption and of stifling opposition.

Kyagulanyi attracted a youth following through songs critical of Museveni and his prominence rose due to an incident in August in which his driver was shot dead and he was detained and charged with treason over what authorities said was the stoning of the president's convoy.

The politician, who has pleaded not guilty to the treason charges, said he was beaten with an iron bar in detention in northern Uganda. The government denies that he was mistreated.

Police had banned rallies to welcome Kyagulanyi home and said on Wednesday that they would escort him to his home in the capital. The legal basis for the escort was unclear, and Kyagulanyi wrote on his Twitter feed before flying home that he should be able to travel freely in his country.

Witnesses said the road linking Kampala to Entebbe town about 50 km (30 miles) to the south was cordoned off, with armed police surrounding the airport.

They also said that all vehicles leaving Kampala on the road to Entebbe were checked at multiple roadblocks. Police prevented journalists from travelling to the airport to cover the arrival.