Police and soldiers fired water cannons and plastic bullets as thousands of students protested against a law passed by Venezuela's congress that increases the government's powers over universities.
At least four people were injured on Thursday, including a photographer who was treated for a cut to the head after being hit with an object.
Dozens of police and National Guard troops in anti-riot gear blocked protesters including students and professors outside the Central University of Venezuela in Caracas, firing plastic bullets into the air and also at demonstrators.
The law governing universities was approved by the National Assembly on Thursday and students condemned it as an attempt by President Hugo Chavez to clamp down on autonomous state universities that have been a bastion of opposition to his government.
Mr Chavez condemned the protest, accusing the group of "trying to lead us into violence". "We don't want violence. We want them to let us work in peace," he said on state television as he visited a hospital.
The law gives Mr Chavez's higher education minister broad powers to decide on academic programmes and university operations, and says universities should promote education that reinforces the government's aim of building a "socialist homeland".
Anti-Chavez protesters say the law gives too much power to the national government and also seeks to impose socialist ideology.
"They won't take away our right to protest," the protesters chanted. "Long live the university! ... Out with the military boot!"
The students had planned to march to the National Assembly but were turned back. Later, hundreds of students managed to continue the march through Caracas on another route, evading authorities who were firing plastic bullets and a water cannon, and shouting: "People, listen! This is a dictatorship!"
The protest ended peacefully once they circled back to Plaza Venezuela near the university.