At least 14 Mexican marines were killed when their helicopter crashed during the arrest and transport of a drug lord in northern Mexico, the Mexican Navy said.
The Black Hawk helicopter, owned by the Navy, was escorting another aircraft carrying Rafael Caro Quintero, founder of the Guadalajara Cartel, who was arrested earlier in the day in the northern state of Sinaloa.
One person survived the crash that occurred on Friday, the cause of which has yet to be determined, Xinhua news agency said quoting the Navy.
The Navy "laments the deaths of those who lost their lives in this accident," it said, adding, "as of now, there is no information linking the plane crash to the arrest of the alleged drug trafficker."
The United States is after Caro Quintero and seeks to extradite him for the murder of Enrique Camarena Salazar, an agent of the US Drug Enforcement Administration (DEA), in 1985.
Due to the Camarena case, "relations between Mexico and the United States were tense" for a time, former DEA agent Hector Berrellez told Xinhua in an interview.
Caro Quintero, a fugitive for many years, was discovered by a sniffer dog hiding in bushes in the town of Choix, Sinaloa, said the Navy.