Uganda's opposition candidate Bobi Wine said he was beaten alongside his aides and supporters by security forces while campaigning in the country's north, in an escalation of violence ahead of the country's presidential election on January 15.

Wine, a pop star-turned-politician, whose real name is Robert Kyagulanyi, is challenging 81-year-old President Yoweri Museveni for the second time after coming second in the last election in 2021.

In a series of posts on his X account late on Saturday, Wine said he was hit in the face with a cane and that other supporters were also beaten and had to be hospitalised, as they approached a campaign venue in Gulu, the biggest city in Uganda's north.

"Criminals in police and military uniform attacked us with sticks and stones and started beating up our people," he said in one post. "One of the thugs hit me with a stick on the face... several comrades are hospitalised. All this because Museveni is dead scared of the people."

Military spokesperson Chris Magezi accused Wine and his supporters of forming an illegal procession and campaigning beyond the prescribed time. "Security forces are there to make sure everyone follows the law," he said.

A police spokesperson did not pick up a Reuters' call seeking comment.

Wine said one of his aides was hit on the head and he posted an image of him with blood oozing from his head. Campaign materials including his public address system had been vandalised, he added.

A video he posted showed what appeared to be a large group of military and police personnel beating people with sticks.

In a statement on Wednesday, U.N. Human Rights Chief, Volker Türk, decried what he described as an "intensifying crackdown" on the opposition in Uganda and said at least 550 supporters of Wine's party, the National Unity Platform, had been detained this year.