CARACAS, Venezuela -- Dissonance from whistles, drums, horns and fireworks accompanied more than a half million Venezuelans who clogged downtown Caracas Thursday demanding President Hugo Chavez's ouster.
Laborers and business executives, leftists and conservatives chanted "Out! Out!" in an 8-mile-long march underscoring the political divisions gripping this South American nation, a top supplier of oil to the United States. Caracas police chief Emigdio Delgado estimated the crowd at 600,000.
Chavez, who was ousted April 12 but restored to power two days later, earlier appealed for calm.
Thursday's march was the fifth and largest since the April coup and followed a peacemaking mission this week by former President Carter.
"The turnout surpassed all our expectations -- maybe even bigger than April 11," Miranda state Gov. Enrique Mendoza said.
Carter's efforts were rebuffed by Chavez's opposition, though Carter did persuade Chavez to accept international mediation in Venezuela's political crisis.
Meeting with military
Several thousand marchers also protested at a Caracas air force base, hoping to meet with military officials. Interior Minister Diosdado Cabello urged them "not to spoil" their peaceful protest.
Several thousand was called by opposition groups commemorating the shooting deaths of 18 people by guardsmen and civilians during an April 11 protest. Hundreds more were wounded.
The violence and Chavez's order to deploy the army prompted dissident generals to oust him the next day. But the leftist Chavez was restored to power in two days on a popular rebellion against an interim government that abolished the constitution.
Dozens died during that weekend of rioting and looting.
Investigations into who committed the April slayings have stalled.
After the coup, Chavez removed unpopular ministers from his Cabinet and offered to change laws opposed by the private sector.
International observers, including Carter Center delegates, monitored Thursday's demonstration.
National guard troops and riot police manned barricades to keep demonstrators away from Chavez supporters and the presidential palace, hoping to avoid bloodshed.
Opponents insist Chavez, a former paratrooper who staged a failed 1992 coup and was elected in 1998, cannot govern the country, which is mired in recession because of low oil prices and political instability.
Venezuela's main opposition parties demand Chavez leave power well before the 2007 end of his term. They have brought court cases alleging corruption, are organizing a referendum on his rule and are demanding justice for the April 11 victims.
"We are on a war footing," said Carlos Ortega, head of Venezuela's largest labor group, the 1 million-member Venezuelan Workers Confederation.
Ortega was surrounded by protest signs reading "No More Deaths" and "Chavez, Assassin."
Ortega, Greater Caracas Mayor Alfredo Pena and other organizers were incensed that the government prevented marchers from going to the palace, which is heavily defended by Chavez supporters.
"We decided to change the route because we have evidence that violent groups were posted near the palace," rights activist Elias Santana said.
Jose Saldana, an unemployed 35-year-old Chavez supporter, said, "Let them come, because they will find a people ready to give their lives for their revolution."
Chavez appealed Wednesday for "calm, prudence and patience. ... My government respects human rights, and I'm sure that there won't be anything to regret Thursday and democracy will be strengthened."
Army commander Gen. Julio Garcia Montoya said troops were on standby in their barracks.
Chavez said Wednesday he would accept an offer by the Organization of American States to help defuse Venezuela's crisis.