Student protesters marching to protest against Venezuela's electoral commission and government have clashed with supporters of the late president Hugo Chavez.
Both sides threw bottles and rocks and scuffles broke out. It was unclear how many people had been injured, but a student leader said at least 10 people from his side had been hurt.
About 300 students were marching through central Caracas when they encountered about 100 Chavez supporters, who began hurling rocks and bottles.
The students returned the volley of objects, and fistfights broke out.
Splinter groups of Chavez supporters tried to attack the students from side streets, but were repelled by plastic bullets and tear gas fired by police.
At one point, about 100 students were trapped by Chavistas who had blocked streets from which they could exit.
"The government activists have ambushed us," said student Vilcar Fernandez. "There wasn't any protection on the part of the security forces."
The students were asking that the commission eliminate requirements that voters have their fingerprints recorded before voting.
They were also demanding the government not interfere in politics ahead of an April 14 vote to replace Mr Chavez.