Gunmen opened fire on students returning from a march in which 80,000 people denounced President Hugo Chavez's attempts to expand his power. At least eight people were injured, including one by gunfire, officials said.

Photographers for The Associated Press saw at least four gunmen -- their faces covered by ski masks or T-shirts -- firing handguns at the anti-Chavez crowd on Wednesday. Terrified students ran through the campus as ambulances arrived.

National Guard troops gathered outside the Central University of Venezuela, the nation's largest and a center for opposition to Chavez's government. Venezuelan law bars state security forces from entering the campus, but Luis Acuna, the minister of higher education, said they could be called in if the university requests them.

Antonio Rivero, director of Venezuela's Civil Defense agency, told local Union Radio that at least eight people were injured, including one by gunfire, and that no one had been killed. Earlier, Rivero said he had been informed that one person had died in the violence.

The violence broke out after anti-Chavez demonstrators -- led by university students -- marched peacefully to the Supreme Court to protest constitutional changes that Venezuelans will consider in a December referendum.

Globovision television broadcast a video of armed men riding motorcycles arriving at the university, where they entered the same building in which several of the gunmen were located. The pistol-toting men stood at the doorway -- one of them firing a handgun in the air -- as people fled the building.

State TV showed footage of angry anti-Chavez students -- many of them with their faces covered by T-shirts -- setting fire to benches and throwing rocks at the university building where the gunmen were hiding before the armed men on motorcycles arrived.

Justice Minister Pedro Carreno blamed students, university authorities, opposition parties and the media for the violence.

"We want to urge the media to reflect, to stop broadcasting biased news through media manipulation, filling a part of the population with hate," Carreno said during a nationally televised address.

He did not provide details regarding the number of injured or if any suspects were arrested, saying only that angry students surrounding the building wanted to lynch those inside.

Student leader Ricardo Sanchez was quoted in Thursday's edition of the local El Universal newspaper as saying a pro-Chavez militia allegedly armed by the government was responsible for the shootings.

"Neither the Metropolitan Police nor the National Guard attacked us during the march, but the Colectivo Alexis Vive, a group of delinquents paid and armed by the government, was allowed to attack students," he said.

University students also staged street demonstrations in the cities of Merida, Maracaibo, Puerto La Cruz, San Cristobal and Barquisimeto on Wednesday. Several of those protests turned violent with rock-throwing students clashing with police shooting plastic bullets at demonstrators.

The amendments being protested would abolish presidential term limits, give the president control over the Central Bank and let him create new provinces governed by handpicked officials.

The protesters demand the referendum be suspended, saying the amendments would weaken civil liberties and give Chavez unprecedented power to declare states of emergency.

"Don't allow Venezuela to go down a path that nobody wants to cross," student leader Freddy Guevara told Globovision during the march to the Supreme Court.

Chavez, who was first elected in 1998, denies the reforms threaten freedom. He says they would instead move Venezuela toward what he calls "21st century socialism."

In televised comments prior to the unrest in Caracas, Chavez urged Venezuelans to turn out en masse to vote for the reforms. "Don't go crazy," he said in reference to Venezuela's opposition.

The Supreme Court is unlikely to act on the students' demands, given that pro-Chavez lawmakers appointed all 32 of its justices.