Petroleum prices rose Tuesday as a strike that has disabled the world's fifth-largest oil exporter entered its 51st day and international mediators struggled to resolve the stoppage aimed at forcing President Hugo Chavez from office.

European Brent crude soared to new two-year highs at more than $31 a barrel because of the Venezuelan crisis, possible war in Iraq and cold weather in the United States.

The Organization of Petroleum Exporting Countries, meanwhile, said it will be difficult to make up for shortages of Venezuelan oil in the United States because many U.S. refineries are geared to process heavier Venezuelan crude.

The strike has slashed Venezuela's oil production by more than two-thirds and caused domestic shortages of gasoline, food and drinking water. It has cost Venezuela $4 billion, according to the government, and contributed to the plummeting of the bolivar currency.

Former President Jimmy Carter was in Caracas trying to help resolve the situation. He was meeting with Chavez at the presidential palace early Tuesday.

Carter, who won the Nobel Peace Prize in October, attended negotiations between the government and opposition Monday and met separately with the president, strike leaders and Organization of American States secretary general Cesar Gaviria.

Carter's Atlanta-based Carter Center, the OAS and the United Nations are sponsoring the talks.

Business leaders, labor unions and opposition parties launched the strike Dec. 2 to demand that Chavez resign or call early elections.

Chavez threatened Sunday to walk out of talks, accusing the opposition of trying to topple him even as they negotiated.

Strike leader Carlos Ortega said Chavez would never accept a vote on his rule.

Ortega, president of the 1 million member Confederation of Venezuelan Workers, said Gaviria and Carter should "convince themselves once and for all that we are dealing with a regime that is not democratic, and that as long as Chavez stays in power there is no possibility of holding elections."

One man was killed and 27 were injured Monday when gunfire erupted as Chavez supporters confronted opposition marchers in Charallave, a town about 20 miles south of Caracas. At least six people have died in political violence since the strike began.

Six countries — Brazil, Chile, Mexico, Portugal, Spain and the United States — have begun an initiative called "Friends of Venezuela" to help end the crisis. Diplomats from the six nations will meet at OAS headquarters in Washington on Friday.

The National Elections Council, accepting an opposition petition, agreed to organize a Feb. 2 nonbinding referendum asking citizens whether Chavez should step down.

Chavez says the vote would be unconstitutional and his supporters have challenged it in the Supreme Court. But the president has welcomed a possible binding referendum halfway through his six-year-term, or August, as allowed by the constitution.

The 48-year-old Chavez was elected in 1998 and re-elected in 2000 on promises to redistribute the country's vast oil wealth among the poor majority.

His opponents accusing him of steering the economy into recession with leftist policies and running roughshod over democratic institutions.