A widespread blackout enveloped much of Venezuela in darkness on Thursday night, stopping subway service in the capital and causing problems around the country, which has been plagued by power failures as its economic crisis has worsened.

The power failure appeared to be more severe than others, however, and the government of President Nicolás Maduro moved quickly to blame its opponents.

The minister of electrical power, Luis Motta Domínguez, said on state television that the blackout was caused by an “attack” on the Guri Dam, a large hydroelectric facility in east Venezuela. Information Minister Jorge Rodríguez, also on the state news network, said that right-wing “criminals” had committed “sabotage” to the dam’s system of generation and distribution.

The officials did not say how much of the country had been affected by the blackout.

Mr. Maduro accused the United States of orchestrating the power failure, writing on Twitter, “The electrical war announced and directed by the imperialist United States against our people will be defeated.”