Mexican authorities said Friday that an alleged regional Zetas drug gang leader captured this week was a key suspect in the killing of a US immigration agent last year.

The army captured Luis Jesus Sarabia Ramon on Wednesday, along with an accomplice, without a shot being fired, according to army spokesman Ricardo Trevino.

He was allegedly in charge of operations in the northern and central states of Coahuila, Aguascalientes and San Luis Potosi for the brutal Zetas gang.

Authorities said he led criminal activities in the violent northern states of Nuevo Leon and Tamaulipas at the time of his arrest and had ordered at least 50 killings as well as kidnappings and extortion.

US agent Jaime Zapata was killed on a highway in San Luis Potosi last February. Another agent, Victor Avila, was injured.

Sarabia was allegedly the boss of Julian Zapata, who has been extradited to the United States on charges of shooting at the US agents.

Authorities said he was close to Zetas leaders Heriberto "El Lasca" Lazcano and Miguel Trevino Morales, alias "Z 40."

The Zetas, who started out as hitmen working for the Gulf cartel in the 1990s, have been accused of a string of killings, kidnappings and macabre brutality that have made them one of the most feared gangs in Mexico and Guatemala.