Uganda’s leading opposition leader returned home on Wednesday from four years of self-imposed exile in South Africa.
Retired Col Kizza Besigye, a runner-up in the 2001 presidential elections, said he had returned to challenge what he called the "dictatorship" of President Yoweri Museveni in the elections expected to take place next year.
He did not however state whether he will stand, only maintaining that the opposition parties will cooperate in order to defeat the current government.
The former army officer fled to exile after alleging that his life was in danger.
"I am coming back, but I know the situation is not different from when I left," he told a news conference immediately he arrived at Entebbe airport, adding that his supporters had been harassed in his absence.
"Political persecution is rampant in this country," he added, calling on Uganda's fractured opposition groups "to co-operate".
He added: "I don't have animosity against the person of the president. We have animosity against his system."
Besigye, who was Museveni's personal doctor during the guerrilla war that ousted Milton Obote and brought Museveni into power in 1986, had been named by government officials as having links to Ugandan rebel groups.
"Our bottom line demand is for essential political reforms," he said. "I am looking forward to a successful break of the vicious cycle that has bedeviled our country for decades."
A government statement issued earlier said Besigye was free to return to Uganda, adding that it was now the Ugandan government policy to reconcile the citizens so that none would remain in exile.
Scores of supporters looked on as Besigye left in a convoy of cars on a journey to the capital, Kampala, that was stopped several times by thousands of people who lined the road from the airport.