Opposition leaders in Venezuela have extended their general strike for a fifth day, as key oil operations in the world's fifth largest exporter ground to a halt because of the job action. The opposition-led strike is aimed at forcing populist President Hugo Chavez to call an early election.

The head of Venezuela's largest labor confederation, Carlos Ortega, made the announcement extending the strike for a fifth day to loud applause from supporters. Mr. Ortega said the decision was the result of what he called the overwhelming response to the job action.

The strike, which began Monday, is being led by an opposition coalition made up of labor, business, and political parties. It is aimed at forcing President Chavez to call early elections.

The strike, which had mixed effects early in the week, extended more deeply into Venezuela's vital oil industry Thursday, despite warnings by President Chavez that his government will not tolerate disruptions.

Oil tanker loadings at most Venezuelan ports were halted following a widespread walkout by managers and administrative staff of the state oil firm, known by its Spanish acronym, PDVSA.

Several PDVSA tankers also joined the strike, halting in Lake Maracaibo in western Venezuela, and refusing to deliver their oil supplies.

One rebel tanker was boarded Thursday by the navy, after the Venezuelan leader announced he will use the military to stop what he called the sabotage of the country's oil industry. He denounced the opposition for attempting to destabilize the country by undermining PDVSA.

Petroleum is critical to the Venezuelan economy, accounting for 75 percent of total exports and half the government's income. Because Venezuela is the world's fifth largest oil supplier, Thursday's events caused petroleum prices to jump by two percent on international markets.

Pro and anti-Chavez rallies were held Thursday in Caracas at two different PDVSA buildings in the city. Several hundred pro-Chavez supporters gathered at one building, vowing to defend the right of oil workers to stay at their jobs.

Xavier Garcia, a systems engineer, told VOA the oil industry must be protected. "The industry is in danger," he said. "I'm no oil expert but I do know that if we cannot comply with the international shipments we have to deliver that's going to get us, the whole country, in trouble. But that's another thing, most of these guys have their capital in the United States. They don't have their money here in Venezuela, so they don't care if this country sinks because their money is all in the United States."

Another pro-Chavez supporter Gabriel Tiro applauded President Chavez' measures to protect the oil industry, saying petroleum represents the life-blood of Venezuela.

On the other side of the city, a larger rally of anti-Chavez demonstrators defended the strike and it's effects on oil exports. Medical doctor Yulie Kertznus compared the current situation to an operation, painful but necessary.

"If you want to have something good, you have to have some pain. If you have a gall bladder disease, and you need an operation, that operation will give you some pain but after the pain you will be completely cured. And that applies to this country," he said. "We need some pain and after that we'll have a good future."

Strike organizers accuse the populist leader of driving the oil-rich nation to ruin because of what they say are his leftist economic and social policies.

They have called on Venezuelans to stage protest actions to show their discontent with the Chavez government.

Mr. Chavez was overwhelmingly elected President in 1998, and again in 2000 under a new constitution, on promises to end corruption and alleviate poverty that affects 80 percent of the population. However, since then, his popularity has plummeted according to opinion polls.

The Venezuelan leader was briefly ousted in April by dissident military officers, but then was restored when loyalist troops and his supporters swept him back into power.

Mr. Chavez Thursday accused the opposition of trying to recreate the events of April, but urged Venezuelans of all social classes to support the constitution and Venezuela's institutionality.