Falcon rejected the result, calling it "illegitimate" on social media.
Venezuelan President Nicolás Maduro, the political heir of Hugo Chávez, won another six years in office in a presidential election on Sunday that was condemned as a farce. It said he defeated Henri Falcon by more than 40 points.
Falcon accused the Maduro government of buying votes and dirty tricks to increase the number of poor Venezuelans voting.
And he added: 'It is beyond satire that still in London you have an official opposition party that refuses to condemn Maduro, refuses to condemn what happened in the elections, which were very far from free, which were obviously rigged, obviously fraudulent and whose analysis - as far as I understand - it is that the problem is not that Venezuela is too socialist but that Venezuela was not socialist enough.
Trading of Venezuelan government and PDVSA debt was mixed but volumes remained thin in NY on Monday afternoon, with election results considered a formality and offering little to change investor viewpoints. He urged the president against being a candidate in a re-vote. Since then, Maduro has presided over an economy in freefall, which has spawned hyperinflation, widespread hunger and an exodus of economic refugees.
London-based Capital Economics said that after Maduro's win "an escalation of United States sanctions seems inevitable".
Several G20 countries announced on the sidelines of a meeting in Buenos Aires that they were mulling sanctions.
For his part, Maduro called on his opponents to recognize the election result and join him in a dialogue for "national reconciliation". Chile had already said it wouldn't recognize the victory, along with Panama and Costa Rica.
But Cuba and El Salvador, two allies of Venezuela, sent their congratulations on the vote.
"In this new term, Turkey will continue to strive to improve its relations with Venezuela in all fields and to support the friendly people and the government of Venezuela".
Venezuela was once home to about 400,000 ethnic Chinese, but a huge percentage of them had returned home over the past four years as its economy imploded and locals became hostile towards immigrants, Hou said.
"The United States stands with democratic nations in support of the Venezuelan people and will take swift economic and diplomatic actions to support the restoration of their democracy", Pompeo said in a statement. Countries in the program pay only a portion of the cost of Venezuelan oil upfront and finance the rest over 25 years at low interest rates.
Venezuela's oil production - the source of nearly all of its overseas earnings - has collapsed to its lowest level.
A USA official said the measures close a set of loopholes, especially those involving debt owed to the government.
Information for this article was contributed by Jorge Rueda and Fabiola Sanchez of The Associated Press.
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