Mr. Carvajal is wanted for similar crimes himself, having been accused of taking money from a Colombian drug trafficker in an indictment that was unsealed in 2014. In 2008, the U.S. Treasury Department sanctioned Mr. Carvajal, who was then head of the country’s military intelligence agency, for “protecting drug shipments from seizure by Venezuelan authorities” as well as providing weapons to the Revolutionary Armed Forces of Colombia, then the country’s main rebel organization.

Image Hugo Carvajal, a former spy chief in Venezuela, was arrested in Spain on Friday. Credit... Fernando Llano/Associated Press

In the February interview, Mr. Carvajal denied the charges, saying he had been in touch with the rebels only to negotiate for the release of a Venezuelan businessman they had kidnapped. He had not been involved in drug trafficking, he said, but repeatedly reported suspicious cocaine shipments to top officials, who ignored them.

Mr. Carvajal, who goes by the nickname “el Pollo,” or “the Chicken,” in Venezuela, made a dramatic public defection from his government by video, urging his former military comrades to rise up against Mr. Maduro and support Juan Guaidó, the leader of the opposition. Few followed his call, however, and Mr. Carvajal’s whereabouts have been unknown since.

His reappearance Friday in the hands of Spanish authorities may lead to his transfer to U.S. custody — and to prosecutors eager to interrogate him on the wrongdoing he has alleged by those in Mr. Maduro’s inner circle.

American authorities’ attempts to capture Mr. Carvajal have stretched on for years.

In 2014, after being appointed as the country’s general counsel to the Caribbean island of Aruba, officials there arrested him, raising hopes with their U.S. counterparts that he would soon be extradited. Aruba originally said that it never accepted his diplomatic post and that he was not protected by it from arrest.