|The teenager told reporters he had worked for a drug cartel since the age of 11 [Reuters]
The Mexican army has detained a 14-year-old US citizen suspected of acting as a killer for a drug cartel.
The boy, nicknamed "El Ponchis," meaning "the cloak" in English, said he had been working for the cartel since he was 11.
He was captured along with his 16-year-old sister late on Thursday night at an airport near Cuernavaca, a city in the state of Morelos.
The pair were trying to catch a flight to Tijuana and planned to flee the country, an army official said.
The sister told journalists that they planned to cross the border to San Diego, California, to go to their stepmother's house.
She said their mother had sent money for the tickets, but she did not specify where the mother lives.
Marco Adame Castillo, the Morelos state governor, said at a news conference on Friday that the boy was born in San Diego and that Mexican officials are researching whether he is a citizen of Mexico as well.
Although state courts usually handle crimes by juveniles in Mexico, state authorities have asked the federal government to take over the case because of the gravity of the crimes.
The teenager told reporters that he had worked for a drug cartel since he was 11 and that he had participated in at least four decapitations.
The source said his sister was accused of getting rid of the bodies by dumping them on streets and motorways.
"I participated in four executions, but I did it drugged and under threat that if I didn't, they would kill me," said the boy.
Another teenage sister accompanied the two, but officials said she was not suspected of being involved in the cartels.
The attorney general for Morelos state said the siblings would be turned over to state authorities, who handle crimes committed by minors in Mexico.
The two were suspected of helping the South Pacific cartel headed by Hector Beltran Leyva, brother of Arturo Beltran Leyva, a top drug lord who was killed by Mexican marines in Cuernavaca a year ago.
Hector Beltran Leyva's fight for control of the cartel has caused a major increase in violence in Morelos, located just south of Mexico City, and in neighbouring Guerrero state.
The brother and sister were living in a poor neighbourhood of Jiutepec, a working-class suburb of Cuernavaca, known as a weekend getaway for Mexico City residents.
Neighbours said the mother had worked in the San Diego area for some time, but none had information about the teenagers' father.