Fistfights and chair-throwing broke out in Uganda's parliament on Tuesday ahead of a debate on whether to grant long-serving President Yoweri Museveni another term in office, local television showed.
The move to extend his rule has met widespread opposition from civic rights activists, the political opposition, religious leaders and even some members of Museveni's own ruling party. He has been in power for more than three decades.
Government and opposition lawmakers came to blows after the House speaker allowed a ruling party legislator to introduce a motion to kick-start a process to remove an age cap from Uganda's constitution to allow Museveni to run for re-election.
Under the existing constitution, a person standing for President must be under 75 years of age - which would make Museveni, 73, ineligible to stand at the next polls in 2021.
Before the parliamentary session, which started at around 1130 GMT, police fired tear gas to disperse protests by students and other opposition activists in the capital Kampala, police spokesperson Emirian Kayima said.
"Some students and other young people were causing commotion and attempting to rob shopkeepers. We engaged them with teargas," Kayima said.
Nineteen people including Uganda's leading opposition figure, Kizza Besigye, were also arrested. Kayima said Besigye was taken into custody after he attempted to mobilise protesters to march on parliament.
"Please take your seats ... let us speak with our words, not with our fists," Speaker Rebecca Kadaga said as she tried to calm the enraged lawmakers.
Police have deployed in force around parliament and throughout Kampala since last week when the move to launch the constitutional amendment process was expected to start but never made it to the floor.