CUERNAVACA, Mexico (Reuters) - Soldiers captured a 14-year-old U.S. citizen suspected of being a drug gang hitman as he attempted to travel to the United States.

Edgar Jimenez, known as "El Ponchis," is believed to work for the South Pacific drug cartel in Morelos state, outside Mexico City, the army said on Friday.

The boy was caught late on Thursday as he boarded a plane in the city of Cuernavaca. He was traveling to the border city of Tijuana with two of his sisters, one of whom is believed to be the lover of one of the cartel's bosses, the army said.

"El Ponchis" made headlines last month as reports of his grizzly murders, including beheadings, surfaced. He acknowledged having killed at least seven people under the influence of drugs provided by a cartel leader, according to the army statement.

The Mexican daily newspaper La Razon said in November that "El Ponchis" was paid $3,000 for each murder he committed.

The three Jimenez siblings had wanted to cross to San Diego, where they have relatives.

Murders committed by minors, ranging from shoplifting to murder for the cartels, have risen across Mexico this year, state officials say. Parents in the violent cities of Ciudad Juarez and Tijuana on the U.S. border say children as young as 8 want to grow up to be drug lords, as the thrills and wealth of the trafficking world touches their lives.

(Reporting by Margarito Perez; Writing by Cyntia Barrera Diaz; Editing by Bill Trott)