Early Tuesday National Guard troops in central Aragua prevented some seven autobuses taking students at Carabobo University (UC) and Libertador Pedagogic College (UPEL) to Caracas, where they are supposed to join a demonstration to reject the planned changes to the Venezuelan Constitution.

Students reacted by blocking the traffic in the highway.

UC student Carlos Azuaje said National Guard troops stopped their autobuses claiming there was a traffic jam, but the troops allowed other autobuses, trucks, and cars to move.

"I talked to a captain who did not provide his name and told me 'Look, man, you are not passing through because that is the order we were given, and period,'" Azuaje told reporters.

University students are staging a march from the campus of the Central University of Venezuela (UCV), northeast Caracas, to the headquarters of the Venezuelan Congress, downtown Caracas. They are demonstrating against a number of changes both President Hugo Chávez and the Legislature are introducing to the Venezuelan Constitution.