Burundi's state prosecution has charged 65 protesters with rebellion after they were arrested during clashes calling for the president not to seek re-election.
Arcade Nimubona, state prosecutor, confirmed on Saturday the protesters have been charged for "participation in an insurrectionary movement".
Burundi, which holds general elections in May to elect lawmakers before a presidential poll in June, is a small landlocked nation in central Africa which emerged in 2006 from a brutal 13-year civil war.
Burundi President Pierre Nkurunziza's expected bid for a re-election despite the constitutional limit of two terms has stirred high tensions in the country.
We know the powers are ready to kill us, to imprison us, but we are ready to lose our blood rather than give up this fight.
Police fired tear gas and water cannon after stones were hurled at them during the clash.
Those found guilty of "armed insurrection" could face life sentences.
Pierre-Claver Mbonimpa, a rights activist and president of Burundi's influential campaign group Aprodeh, has condemned the charges.
"It is a political issue, because these people were about to exercise their right under the constitution" to protest, Mbonimpa said.
A large crowd of opposition activists gathered to sing songs outside the court to support those who were charged.
The UN Security Council on Friday had warned the upcoming elections in June could turn violent and vowed to take actions against those creating unrest.
Five opposition parties, as well as splinter groups of the ruling CNDD-FDD who oppose Nkurunziza, have launched a campaign calling for the president not to run again.
Chauvineau Mugwengezo, president of the opposition UPD party, said protests would continue.
"We know the powers are ready to kill us, to imprison us, but we are ready to lose our blood rather than give up this fight," Mugwengezo said.
Nkurunziza, however, has not yet officially declared that he will be running for another term.
His party, the CNDD-FDD is expected to hold a party congress by the end April to nominate its presidential candidate for the polls.