MEXICO CITY (AP) — The U.S. ambassador to Mexico confirmed Friday that drug lord Ismael “El Mayo” Zambada was brought to the United States against his will when he arrived in Texas in July on a plane along with fellow drug lord Joaquín Guzmán López.

Zambada’s attorney had earlier claimed the longtime chief of the Sinaloa cartel had been kidnapped. But officials had not confirmed that and Zambada’s age and apparent ill-health had led some to speculate he turned himself in.

U.S. Ambassador Ken Salazar on Friday said “the evidence we saw … is that they had brought El Mayo Zambada against his will.”

“This was an operation between cartels, where one turned the other one in,” Salazar said. Zambada’s faction of the Sinaloa cartel has been engaged in fierce fighting with another faction, led by the sons of imprisoned drug kingpin Joaquín “El Chapo” Guzmán. Guzmán López is the half-brother of the factional leaders.

Salazar said no U.S. personnel, resources or aircraft were involved in the flight on which Guzmán López turned himself in, and that U.S. officials were “surprised” when the two showed up at an airport outside El Paso, Texas on July 25.

Frank Pérez, Zambada’s attorney, said in a statement in July that “my client neither surrendered nor negotiated any terms with the U.S. government.”

“Joaquín Guzmán López forcibly kidnapped my client,” Pérez wrote. “He was ambushed, thrown to the ground, and handcuffed by six men in military uniforms and Joaquin. His legs were tied, and a black bag was placed over his head.”

Pérez went on to say that Zambada, 76, was thrown in the back of a pickup truck, forced onto a plane and tied to the seat by Guzmán López.

In early August, Zambada made his second appearance in federal court in Texas after being taken into U.S. custody the week before.

Guzmán López had apparently long been in negotiations with U.S. authorities about possibly turning himself in. Guzmán López, 38, has pleaded not guilty to drug trafficking and other charges in federal court in Chicago.

But U.S. officials said they had almost no warning when Guzmán López’s plane landed at an airport near El Paso. Both men were arrested and remain jailed. They are charged in the U.S. with various drug crimes.