Venezuela ? Thousands of university students scuffled with police and government supporters during a protest Tuesday demanding that civil liberties be respected under constitutional reforms being drafted by allies of President Hugo Chavez.

Police tossed tear gas canisters into the crowd of opposition students after clashes broke out with a smaller group of pro-Chavez demonstrators near the National Assembly. Journalists estimated the crowd at about 20,000 protesters, but pro-Chavez lawmakers said there were far fewer.

There were no reports of arrests or serious injuries.

Students said they fear civil liberties would be severely weakened under the constitutional changes under consideration. Critics are particularly concerned by an amendment that would allow authorities to detain citizens without charges during a state of emergency.

The National Assembly, dominated by Chavez supporters, is poised to approve 67 constitutional amendments that would give the government control over the Central Bank, create new types of cooperative property and extend presidential terms from six to seven years while allowing Chavez to run again in 2012.

To take effect, the reforms must be approved by voters in a Dec. 2 referendum.