Several people were wounded in the clashes as police fired bullets and tear gas while opposition supporters hurled rocks and erected street barricades in the capital's Wandegeya suburb, witnesses said according to a Reuters news agency report..
The main opposition leader Kizza Besigye, who heads the Forum for Democratic Change (FDC) party, was held on Monday evening, his second brief detention of the day, after marching with thousands of supporters to a rally in Kampala.He was released soon afterwards, a party spokesperson said.
Stand-off in Kampala
Police said Besigye was held because he did not stick to an authorised route, and his diversion would disrupt businesses.
"Police can confirm one person died during the confusion today," Kampala police spokesman Patrick Onyango told the AFP news agency, without giving further details.
Opposition politicians told AFP that three people had been shot dead, but the claims could not be independently verified.
FDC spokesman Semujju Nganda said "several" supporters were injured during scuffles with police.
"We protest in the strongest terms police brutality towards our supporters

and targeting our candidate," he said.
But Frank Tumwebaze, minister for the presidency, said it was "madness" that Besigye had tried to hold a rally in the centre of the capital, saying the police had a duty to ensure calm.
He accused Besigye of "seeking publicity ... after sensing defeat ahead".


The outbreak of violence came just three days before presidential and parliamentary elections are due to take place on February 18.
Coleen Nantongo, an FDC parliamentary candidate for Kampala Central, said the unrest cast a dark cloud over the upcoming polls.
"Uganda is doomed," she said. "We cannot have a fair election when this is what the police do. Whenever there are elections they tear gas us and arrest us, so how can we be expected to have a fair competition?" 
Earlier in the day, Besigye, who has lost three disputed elections against long-running president Yoweri Museveni, was also briefly detained for leading a procession of supporters in Kampala.
Opposition supporter James Magara, 40, said that the arrests raised doubts that the election would be free and fair.
"There is no democracy in Uganda, and now the whole world will see it. Museveni does not want to lose so he sends the police after us, but this time we will not accept it. We will not let him continue like this," 
Students demonstrating at Makerere University in Uganda's capital, Kampala [Tendai Marima/Al Jazeera]
Although parts of the campaign period have been relatively peaceful in Kampala, the international community has before raised concerns over repression of opposition figures.
In October 2015, Besigye was placed under what the police called "preventive arrest" after a series of protests over high fuel prices.
Museveni has been in power since 1986.