Venezuelan National Guard troops fired tear gas in Caracas today to keep apart supporters of President Hugo Chavez and opposition marchers who were protesting the military takeover of the city police.

Troops and police moved into action as thousands of anti-government demonstrators advanced to a few blocks from the National Assembly, a stronghold of support for Chavez, who was elected in 1998.

The march, the latest in a series of protests against the president that began a year ago, raised fears of renewed violence. Chavez, who survived a brief military coup in April, is resisting pressure to quit and hold an early referendum on his rule.

Opposition leaders have threatened to call a nationwide general strike soon if he ignores their formal request for an immediate referendum, backed by more than 2 million signatures.

Chavez says the constitution does not allow this kind of referendum until next August.

Government and opposition negotiators, who are struggling to keep alive peace talks brokered by Cesar Gaviria, the secretary general of the Organization of American States, appealed for calm.

Separated by troops and police, pro-Chavez militants yelled, "They will not pass!" and shouted insults at the opposition marchers, who replied by chanting, "Not one step backwards!"

As the two sides came close to clashing on University Avenue, the National Guard fired tear gas to disperse them.

In a speech, Chavez played down the unrest. "The country is working; we are pumping two million barrels of oil a day," he said.