Venezuelan authorities on Monday began a partial audit of the disputed election won by the late Hugo Chavez's handpicked successor, as the opposition rejected the move as insufficient.
Opposition leader Henrique Capriles, who says he was the real winner of the April 14 presidential vote, has accused election officials of rejecting his appeal for a full recount on the orders of the ruling Socialist Party.
The National Electoral Board has ruled that President Nicolas Maduro -- the leftist heir to the late Chavez -- won by 1.49 percent of the vote, amending an earlier tally that had Maduro up by 1.8 percent.
The Board has insisted it is legally impossible to carry out a full recount, and that no audit can reverse Maduro's win.
The 40-year-old Capriles has said he will not accept anything short of a full recount, and in a Twitter posting on Monday he lashed out at Maduro, 50, calling him a "laggard who illegitimately has stolen the presidency."
Ruling party leader Diosdado Cabello meanwhile questioned the holding of the audit -- which could last until early June -- "when the party who requested this is not even taking part."
Capriles now appears focused on seeking a new election while taking the fight to international arenas.
"The next step, as I have indicated, will be for me to request annulment of the results, and in so doing eliminate the matter legally as a domestic issue," Capriles said. He has until May 6 to take his fight to the Supreme Court.
"I have no doubt that this will end up before an international body," Capriles added.
Capriles -- a businessman, lawyer and Miranda state governor -- alleges that some voters cast multiple ballots or even voted on behalf of the dead.
Both the government and the opposition have urged their supporters to turn out for massive street protests planned for May 1.
Spain has meanwhile offered to mediate between the two sides "to guarantee peace, prosperity and stability in Venezuela," top diplomat Jose Manuel Garcia Margallo said in Washington.
There was no immediate reply from Caracas.
Chavez, the most prominent face of the Latin American left for over a decade, was Venezuela's president for 14 years before his death last month.
Venezuela sits atop the world's largest proven oil reserves, and Chavez had harnessed its wealth to support popular social programs and provide aid to fellow leftist leaders across the region.
Maduro, a former bus driver and union organizer, was a member of Chavez's inner circle throughout the late leader's reign, serving as his vice president and foreign minister.