Thousands of people wearing red berets marched Saturday through the capital of oil-rich Venezuela to support embattled President Hugo Chavez a day after three people were fatally shot at an opposition rally.

Demonstrations by both sides of Venezeula's political conflict had police worried of increased violence after gunmen opened fire Friday night into a plaza crowded with opposition demonstrators. In addition to the three deaths, 28 people were wounded.

The killings caused the opposition — until now seeking only a referendum on Chavez's 4-year-old government — to demand his resignation. Leaders declared three days of mourning, calling for nationwide protests and the extension of a general strike that has already shut down Venezuela's giant oil industry.

Police patrols in Caracas were drastically cut a month ago when Chavez seized control of the city force. Citing the threat of violence, the U.S. State Department on Saturday urged Americans not to travel to Venezuela.

The United States depends on Venezuela for more than 10 percent of its crude oil imports. A prolonged shutdown — coupled with the threat of war in Iraq — could drive up U.S. energy prices.

Pro-Chavez crowds chanted "Chavez drives them crazy!" — referring to the opposition — as they marched to the presidential palace.

"I had to come to show my rejection of the way the opposition is always blaming innocent people for the violence," said Peggly Martinez, 19, a university student. "There's no dictatorship here and we want the world to know it."

Chavez, a former army paratrooper who led a failed 1992 coup, was overwhelmingly elected in 1998 by promising to eliminate a corrupt democratic system that failed to distribute oil riches to the poor. He was re-elected to a six-year term in 2000.

His popularity suffered as his "peaceful revolution" against poverty produced few results. Venezuela's economy shrank 7 percent this year, despite relatively high oil prices. Inflation is at 30 percent, unemployment at 16 percent. More than half the work force does not have a full-time job.

Chavez's approval among the poor — his core constituency — has slipped to about 45 percent in recent polls, while his overall support hovers around 30 percent. He has the support of Bolivarian Circles, neighborhood groups that carry out social projects and other government-backed actions. In the past, radical armed members of the group have attacked opposition marches, politicians and journalists.

Chavez appealed for calm after Friday's shooting at Plaza Francia, an opposition rallying spot since dissident military officers occupied it in October.

He denied claims that he was behind the attack, which occurred moments after the opposition said it would extend its strike. Chavez asked U.S. former President Carter, who has tried to mediate in Venezuela, to help calm tensions.

The Organization of American States called for emergency talks between the two sides late Saturday. U.S. Secretary of State Colin Powell phoned mediator Cesar Gaviria, secretary general of the organization, to express his support for the talks, U.S. Ambassador Charles Shapiro said.

A stumbling point is the opposition demand that Chavez call a nonbinding referendum on his presidency. Venezuela's constitution says a binding referendum may be held halfway into his term, or next August.

Chavez said Saturday that the national elections council, which has approved a Feb. 2 referendum, must be changed "so we have someone impartial" to conduct elections. His government insists a constitutional amendment is needed to call an early referendum.

Timoteo Zambrano, an opposition negotiator, said the opposition would now demand Chavez's immediate resignation at the talks. The general strike was non-negotiable, he said.

Chavez, whom dissident military officers ousted briefly in April, accused the opposition of trying to provoke another coup.

At a news conference Saturday, Chavez said he could decree a state of emergency if the strike was extended. "It's a possibility, depending on the evolution of the situation," he said.

Inside Venezuela's oil industry — the world's fifth largest — all seven directors of the state-owned Petroleos de Venezuela S.A. oil company offered their resignations to protest the board appointment of a Chavez ally, Alfredo Riera, said dissident manager Juan Fernandez.

Chavez said his government was in the process of replacing striking oil company managers and tanker crews. He said "international clients haven't been affected, although there are some delays" in shipments.

The president warned that "some television stations are very close to committing crimes" for their overt support of the strike. Just before he was ousted in April, he shut down private stations.

The three days of mourning began with hundreds of opposition protesters in black clothing gathering at Plaza Francia. Confusion increased as protesters wrested handguns from two people in the crowd they called "infiltrators."

Enraged by the pro-Chavez march, the opposition Democratic Coordinator political movement issued a statement accusing the government of having "declared war against the people."

City heath department chief Pedro Aristimuno said Friday's attack killed a 17-year-old girl, a 70-year-old woman and a 44-year-old man. Twenty-eight people were wounded, all by gunshots.

Attorney General Isaias Rodriguez said seven people were in custody, including a minor. Authorities said one suspect confessed to shooting at the crowd. Accusations against other detainees — including British citizen Frank Pietersz — were not clear.

Police confiscated a pistol from taxi driver Joao de Goveia, 39, a Portuguese citizen who has lived in Venezuela for more than 20 years, said Leopoldo Lopez, mayor of the Caracas district where the plaza is located. Lopez said Goveia admitted firing about 10 shots into the crowd.

Vilma Calzadilla, 38, was at the plaza Friday with her two children when the shooting occurred.

"I feel like the dead are my family," she said, back at the plaza Saturday to leave flowers.