The United States has declined to join international monitors in backing Venezuelan President Hugo Chavez's apparent victory in a weekend recall election.
The US has called for a prompt, thorough and transparent probe into opposition claims of massive fraud.
Earlier, the European Commission described the conduct of the Venezuelan referendum as a 'victory for democracy'. And former US President Jimmy Carter, who led an observers' mission, verified that President Chavez won the support of 58% of the electorate.
Venezuela's opposition rejected the result, and opposition leader Henry Ramos Allup said the vote was a fraud. He promised to contest the outcome.
Oil prices had fallen from recent record high levels after indications that the referendum would show clear support for President Chavez.
Venezuela is the world's fifth largest oil exporter.
