Appearing on state TV, Nicolas Maduro showed a picture of what looked like a cut conductor cable.
He said the saboteurs’ aim was to destabilize the country ahead of local elections scheduled for this weekend.
Caracas’ metro ground to a halt and people had to be led out of shops and offices – but power was later restored.
Government opponents say poor maintenance was the likely cause of the blackout.
Power cuts are common in Venezuela, especially in the inland states, but they rarely affect the capital.
Speaking on state TV, Nicolas Maduro said that “we always face these attacks by the right-wing fascists”.
“They wanted to make me, as president of the republic, decree a state of emergency and suspend the elections.
“Whoever made this criminal attack wanted to leave our Venezuela without electricity for 24 to 48 hours… thinking that would convince people not to continue with the revolution.”
Nicolas Maduro promised to give more details on Wednesday.
He earlier tweeted that the outage had been triggered in the same place as a blackout in September.
The power cut plunged Caracas into darkness after 20:00 on Monday as Nicolas Maduro was addressing the nation on television.
The blackouts did not affect Venezuela’s oil refineries, which are powered by separate generator plants.
Sometimes after the outage, Electricity Minister Jesse Chacon said power had been restored to most of Caracas. He said the blackout had originated in central Venezuela.
The opposition says the governments of President Nicolas Maduro and his predecessor, Hugo Chavez, have failed to maintain the power grid to meet growing demand, instead resorting to conspiracy theories to divert attention from mismanagement.
Correspondents said that while Caracas was in darkness, people could be heard banging pots – a frequent means of protest.
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