KAMPALA (Reuters) - Ugandan pop star turned opposition politician Robert Kyagulanyi pledged on Thursday to continue what he calls a fight for freedom for millions of oppressed fellow citizens, after returning to his country from the United States.

Ugandan musician turned politician, Robert Kyagulanyi addresses his supporters outside his home after arriving from the U.S. in Kampala, Uganda September 20, 2018. REUTERS/Newton Nambwaya

The return of the 36-year-old musician, known by his stage name of Bobi Wine, has rattled the government headed by 74-year-old President Yoweri Museveni, who has been in power since 1986 and leads a nation where nearly 80 percent of the population is below the age of 30.

Though a political novice -- he was elected in a parliamentary by-election last year -- Kyagulanyi’s popularity has skyrocketed particularly among disillusioned youths who say they see few prospects under the rule of Museveni.

When Kyagulanyi arrived at Entebbe International Airport from the United States, police escorted him into a vehicle and whisked him to the capital Kampala where his whereabouts were for a time unknown, leading supporters for a while to fear he had been arrested.

He had received medical treatment in the United States for injuries which he said were sustained during torture by security forces last month. The government has denied any mistreatment but says it is investigating.

But Kyagulanyi later appeared atop a car outside his home in Kampala to address hundreds of cheering supporters.

“I am resuming immediately ... I am on the mission already, I am on the fight for freedom and liberty already,” he said, surrounded by throngs of people.

Leaning on a cane, he said his “desire for liberty” was as strong as “the desire of the millions and millions of people in Uganda to be free.” Ugandans, he said, were “slaves in our own country”.

His supporters had earlier in the day defied a heavy security presence and gathered at his residence to welcome him, but once he arrived by police escort, security forces did not attempt to stop crowds from gathering at his home.

Slideshow ( 9 images )

Many of his supporters wore red t-shirts and hats. The color has come to be associated with his “People Power” movement, and demonstrators at Ugandan embassies in London, Nairobi and elsewhere have donned the same color during protests.

Police had on Wednesday banned rallies to welcome Kyagulanyi home and said they would escort him to his home. The legal basis for the escort was unclear.

Ahead of Kyagulanyi’s arrival, security forces had deployed around the airport and the highway linking it to Kampala to prevent supporters from greeting him. Armored personnel carriers and police vehicles lined the route and journalists were prevented from traveling to the airport to cover the arrival.

Kyagulanyi is increasingly 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.

Museveni has won praise in the West for his support against militant Islam and his role as power-broker in the volatile Great Lakes Region. Uganda has also welcomed foreign investors such as France’s Total, China’s CNOOC and Britain’s Tullow as part of a plan to start pumping oil from 2021.

But the government is facing growing criticism from its allies, particularly main donors the United States and the European Union, who have deplored the torture alleged by opposition politicians including Kyagulanyi.

Kyagulanyi attracted a youth following through songs critical of Museveni and his status rose higher 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.