Official results from the April 14 elections gave Nicolas Maduro a razor-thin margin of just 1.5 per cent over Capriles.
"The appeal has been declared inadmissible," announced Gladys Gutierrez, president of the Supreme Tribunal of Justice (TSJ), yesterday.
The opposition filed the 10-point appeal three months ago arguing that the vote, held in the wake of longtime leader Chavez's death in March, was marred by fraud.
Among other things, Gutierrez said the plaintiffs did not offer "sufficient proof" to back up their allegations.
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Capriles said Tuesday that he would go "before international bodies" to contest the election.
He did not name any avenue of appeal but said two complaints would be filed, one in his name and one in the name the Democratic Unity Roundtable (MUD), an umbrella coalition for opposition parties.
Despite his questioning of the electoral system, Capriles has said that MUD will nonetheless participate in December 8 municipal elections, so as to not hand the Venezuelan government "a gift.