KAMPALA, UGANDA -- Ugandan police on Monday detained the singer and political activist known as Bobi Wine, who was prevented from holding his first public meeting with supporters as a presidential aspirant.

Police fired tear gas as they dispersed a crowd of supporters outside the capital, Kampala. Gunfire was heard but it was not clear if live rounds or rubber bullets were fired.

The foiled meeting had been authorized by electoral authorities. It was the first of several planned by Wine, a 37-year-old opposition lawmaker whose real name is Kyagulanyi Ssentamu.

Police said he was arrested for showing "blatant disregard for the law" when he tried to convene what they described as an illegal public assembly instead of an indoor meeting.

The statement said organizers have a duty to provide a "traffic assembly plan," a sufficient number of toilets and "clearly identified name tags."

Police did not say whether Wine would face charges.

In a Twitter post, Wine said he and some colleagues in custody had been transferred from a police post in his constituency to one further outside Kampala.

Robert Amsterdam, a lawyer for the activist, said on Twitter that his client and others had been "arrested without reason" and he denounced "this violation of basic rights."

Police have repeatedly prevented Wine from addressing rallies or even organizing musical concerts in recent months, saying the events pose a danger to the public.

Presidential elections are scheduled for 2021. There are growing concerns that campaigns could turn violent as security forces tighten the space available for opposition activists to interact with supporters.

Wine has called for the retirement of longtime President Yoweri Museveni, saying young people must prepare to take over leadership of the East African nation. Museveni, who has indicated he will run again, accuses the singer of trying to lure his supporters into rioting.

Wine came to political prominence nationally in 2017 when, as an independent candidate, he won election as a lawmaker representing a constituency near Kampala. He has since successfully campaigned for other opposition candidates, raising his profile and attracting encouragement to run for president.

But he faces challenges including treason charges related to his alleged role in a 2018 incident in which the president's convoy was attacked with stones at a campaign event. Prosecutors have added charges of annoying the president over that incident. He also is charged with disobeying statutory authority after he led a demonstration against a tax targeting social media. He denies all the charges.

A criminal conviction would prevent him from seeking the presidency.

The 75-year-old Museveni is eligible to run again after lawmakers passed legislation removing a clause in the constitution that prevented anyone over 75 from holding the presidency. Wine was among those who opposed the move.

Uganda has never had a peaceful transfer of power since the country gained independence from Britain in 1962. Museveni has held power since 1986 and is increasingly accused by critics of wanting to rule for life.