Soldiers used tear gas, plastic bullets and water cannons to scatter tens of thousands of demonstrators protesting constitutional reforms that would permit Venezuelan President Hugo Chavez to run for re-election indefinitely.
Led by university students, protesters on Thursday chanted "Freedom! Freedom!" and warned that 69 amendments drafted by the Chavista-dominated National Assembly would violate civil liberties and derail democracy.
It was the biggest turnout against Chavez in months, and appeared to revive Venezuela's languid opposition at a time when the president seems as strong as ever. Students promised more street demonstrations over the weekend.
"This is a dictatorship masked as democracy," said Jorge Rivas, an 18-year-old student. "Chavez wants our country to be like Cuba."
Authorities broke up the protest outside the headquarters of the country's electoral council, reporting that six police officers and one student were injured. But students said dozens of protesters were hurt during the melee. The Globovision TV network broadcast footage of several police beating an unarmed protester with billy clubs.
Student leader Freddy Guevara said it was not immediately clear how many students were arrested.
Students hurled rocks and bottles, and a few lifted up sections of metal barricades and thrust them against police holding riot shields.
"Chavez wants to remain in power his entire life, and that's not democracy," said Gonzalo Rommer, a 20-year-old student who joined in the protest.