MEXICO CITY — The U.S. government on Friday provided the first official explanation of the mysterious flight that carried two Sinaloa cartel leaders to the United States last month, denying that American agents or a U.S. plane took part in spiriting Joaquin “El Chapo” Guzmán’s son and Ismael “El Mayo” Zambada out of Mexico.

       Ken Salazar, the U.S. ambassador to Mexico, said a betrayal in the highest ranks of the cartel was behind the operation.

       The aircraft didn’t file a flight plan with the United States, he said. It took off from Mexico’s western state of Sinaloa on July 25 and landed at the airport in Santa Teresa, N.M., just outside El Paso, he said.

       “We were surprised when that happened,” he said. U.S. officials had previously said that law enforcement agents had scrambled to get to the airport because they didn’t previously know about the inbound flight.

       U.S. and Mexican officials have provided limited, sometimes conflicting accounts about the spectacular capture of the two alleged drug kingpins, and many details remain unclear. Mexican media has speculated that the United States may have violated this country’s sovereignty, an allegation Salazar rejected.

       Zambada is considered a legendary godfather in the Mexican drug trade. He and El Chapo’s son belong to different factions of the Sinaloa cartel. The syndicate is accused of being the No. 1 supplier of fentanyl to the United States, as well as a prodigious wholesaler of cocaine, heroin and methamphetamines.

       Mexican President Andrés Manuel López Obrador complained Friday morning that Washington had kept him in the dark about the operation. “There’s no cooperation from the United States,” he told his daily news conference. “What did they do with the pilot? Who was he? And of course, where did the plane take off from?”

       Hours later, Salazar held a news conference to offer answers. He told reporters that the younger Guzmán, also named Joaquín, had voluntarily given himself up. Initial indications were that Zambada, 76, “was brought against his will” to the United States, he said.

       “This didn’t involve our agents, or our people in Mexico,” he said in Spanish. The operation came about because of friction between factions within the cartel, he added — “and one gave up the other.”

       U.S. officials told The Washington Post and other media outlets last month that Guzmán, 38, had tricked the older cartel capo into boarding the plane, saying they were going to visit potential investment properties in Mexico. But many analysts had cast doubt on the story, noting that Zambada was a cautious, savvy trafficker who’d never been caught, even though he was a target in decades of anti-drug operations.

       Joaquín Guzmán’s attorney, Jeffrey Lichtman, has strongly denied that his client struck a deal with U.S. officials and lured Zambada onto the plane.

       Salazar said that when U.S. authorities realized the traffickers had arrived on American soil, “we were in contact right away with our friends and colleagues in the Mexican government.”

       He said the pilot wasn’t a U.S. citizen or working for the American government but provided no further details about his identity.

       Zambada’s lawyer has said his client was kidnapped by the younger Guzmán. “He was ambushed, thrown to the ground, and handcuffed by six men in military uniforms and Joaquín,” the attorney, Frank Perez, said in a recent statement, reported by the Associated Press.

       “His legs were tied, and a black bag was placed over his head,” Perez said. He added that Zambada was then tossed into a pickup truck and forced onto a plane, where Guzmán tied him to a seat.

       Both Zambada and Guzmán pleaded not guilty to a raft of drug charges in their initial court appearances.

       Guzmán is one of the four sons of El Chapo — known as the “Chapitos” — who inherited his business after the kingpin was arrested in 2016, according to the Drug Enforcement Administration. The youngest of the four, Ovidio, was detained by the Mexican army last year and extradited to the United States.

       An official with the Department of Homeland Security had told The Post that Ovidio, 34, had contacted his older brother from a U.S. prison to plot the downfall of Zambada, in an apparent effort to win favor with American authorities.

       The Mexican government has said it had no role whatsoever in the arrests. It initially provided an error-filled account — telling reporters the pilot involved in the operation was an American who flew the two suspects in a Cessna out of the state of Sonora. In fact, the plane was a Beechcraft King Air, U.S. officials say. Rumors have swirled in the Mexican press about possible involvement by American agents.

       Salazar took pains to scotch such reports and emphasize the close cooperation between the governments. “We have always acted with respect for the sovereignty of Mexico,” he said. “This work as partners, respecting sovereignty, has brought us great results.”

       Nick Miroff in Washington contributed to this report.