Venezuela's Chief Prosecutor Tarek Saab says he has asked the Supreme Court to investigate opposition leader Juan Guaidó for allegedly sabotaging the country's electrical system.
Much of Venezuela has been without power since Thursday afternoon.
President Nicolás Maduro has said that "US technology" was used to sabotage the electricity grid and has pointed the finger at the opposition.
Mr Guaidó says it is down to government mismanagement.
Mr Saab's announcement came just hours after President Maduro had said in a televised message to the nation that "the hour of justice has come" and that the "justice [system] will go after the person behind this criminal attack against the Venezuelan electricity system".
Separately, the US is preparing to impose "very significant" additional sanctions against Venezuelan financial institutions in the coming days, its special envoy Elliott Abrams has said, without giving any further details.
The US has already imposed sanctions designed to curtail Venezuelan oil sales, and has targeted a growing list of individuals and companies linked to the Maduro government.