Listening to embattled President Nicolás Maduro of Venezuela ramble for hours about an international right-wing conspiracy to oust him, it’s clear that he would use any fabricated pretext to jail opposition leaders and crack down on dissent.

In recent days, the government’s claims have become outlandish and its repression of critics even more vicious.

On Thursday, intelligence agents dispatched by Mr. Maduro arrested Mayor Antonio Ledezma of Caracas, the capital, one of the politicians who has been critical of the president. Mr. Ledezma has been charged with conspiracy to help plot an American-backed coup. The arrest came a year after the country’s most high-profile opposition leader, Leopoldo López, was jailed on trumped-up charges that he instigated violent demonstrations.

“You know that the right in Madrid, the ultraright in Bogotá and the ultraright in Miami have forged an axis to conspire against the homeland,” Mr. Maduro said Thursday in a televised address.