Police in Burundi have fired tear gas and water cannon to disperse hundreds of opposition supporters in the capital, Bujumbura.
The demonstrators were calling for President Pierre Nkurunziza not to run for a third term in presidential elections scheduled for June.
A BBC reporter in the city says parents rushed to schools to pick up their children, fearing further trouble.
Mr Nkurunziza has not confirmed whether he plans to seek re-election.
But he is widely expected to be named candidate for the elections by the governing CNDD-FDD party.
Opponents say any plan to do so would violate the country's constitution and a peace accord that ended Burundi's brutal civil war.
The BBC's Ismail Misigaro in Bujumbura says large trucks carrying tear gas could be seen all over the capital.
Crowds of mainly young men chanted "we won't let him run again", as police blocked them from entering the city's Independence Square.
Two police officers were injured during the protests, and several arrests were made, the AFP news agency reports.
The UN refugee agency says more than 8,000 people have fled to neighbouring Rwanda and the Democratic Republic of the Congo in the past two weeks because of "pre-election violence and intimidation".
Some of those who fled have reported the disappearance of family members connected to the opposition.
A former rebel leader, Mr Nkurunziza took office in 2005 following the end of a 12-year conflict, which killed more than 300,000 people.
He was re-elected in June 2010 but the vote was boycotted by the opposition, which complained of fraud in the earlier local elections.
Opposition leaders and international observers have since complained of a growing crackdown on opposition parties and the media.