At least two people have been killed after Ugandan police fired live bullets and tear gas to disperse crowds protesting against the arrest of Kizza Besigye, leader of the country's main opposition party, a Reuters witness says.
Ugandan security officials prevented Besigye from boarding a plane to Kenya on Friday to seek treatment for injuries received during his arrest on Thursday.
"Plain clothes men have blocked him from leaving. We don't know why. They are threatening him with arrest if he does not leave (the airport)," Anne Mugisha, deputy foreign secretary of the the Forum for Democratic Change party (FDC), said.
She said the plane Besigye had been due to board left for Nairobi without him.
One of the victims in Friday's riot appeared to have been shot in the head and was lying in a pool of blood at a local market, a witness said.
Michael Nataka, from the Ugandan Red Cross, said more than 100 people had sought medical attention.
"There are a number of injuries. Some, about 21 of them, have bullet wounds. Then we have people who have been affected by tear gas, there are those who have injuries as a result of stones, they were hit by stones," he said.
"Then we have those who look like they were beaten, either by batons or sticks. Then we have those who were injured as a result of falling down as they were running." Nataka said.
Local media reported a third person had been killed in the riot, but the claims could not be independently verified.
Smoke billowed over the capital Kampala after crowds burnt tyres to block roads.
Protesters stoned shops and cars to express their anger at Besigye being beaten, pepper-sprayed and dragged away by police, all shown on TV.
Besigye, who was a runner-up to veteran president Yoweri Museveni in a disputed February election, was arrested and later freed on bail for his role in leading the ongoing protests against soaring fuel and food prices.
The protests - dubbed "walk to work" in solidarity with Kampala residents who cannot afford public transport as a result of high fuel prices - have been joined by several opposition politicians, one of them still in detention.
Besigye's arrest, the fourth time in three weeks he has been detained, followed a week of detention in a countryside prison where he was held with three of his supporters and the head of the Democratic Party, Nobert Mao.
The leader of the FDC, who has previously been detained on trumped-up charges of rape and treason, said he was leading peaceful protests and that he and his supporters had the right to protest.
"We shall continue protesting within the law [and] peacefully. None of us is armed," he said while seated on the back of a police pick-up truck, his right hand hit by a rubber bullet a week ago still heavily bandaged.
'Misuse of resources'
Uganda's opposition has termed the government's decision to spend $720 million on Russian fighter jets - when people are starving - a misuse of meagre resources.
"How can they tear gas and beat an important man like [Besigye] when he is telling the truth that we are poor? They spend our money on fighter jets and tear gas when people have no food," shouted an angry protester who only gave his name as Stephen.
A witness in Kampala told Al Jazeera by email that chaos had engulfed the city.
"Things are not good here. I can still hear occasional gun shots from where I am. The TV is saying about 90 injured persons with bullet wounds have been taken to Mulago hospital," said Moses Odokonyero.
Besigye's supporters carried posters praising him, and questioning why police need to use violence to arrest him.
A police spokeswoman, Judith Nabakooba, said that Besigye was arrested for not following police orders and for leading a chaotic demonstration
The protest held up traffic and saw Besigye's supporters hurl stones at passing vehicles, she said.
President Museveni, in power since 1986, blames drought for high food costs and soaring global oil prices for surging local fuel costs, and has warned Besigye that his protests will not be tolerated.
Besigye lost the February 18 presidential election for a third time and has vowed to continue campaigning despite repeated detentions during the protests that have killed at least six people.