CUERNAVACA, Mexico — In cargo pants and a T-shirt, the skinny, American-born 14-year-old looked like he should be in middle school. Instead he was surrounded by three armed Mexican soldiers in ski masks and camouflage as he told reporters that he helped a Mexican drug gang behead four people.

Mexican officials say they arrested the youth known as "El Ponchis" late Thursday at an airport south of Mexico City with a 19-year-old sister who is accused of helping him dump the bodies. Authorities said he was caught with two cell phones that held photographs of tortured victims.

Many youths have been used by drug cartels in their bloody battles against the government and each other, but the story of El Ponchis may be the most shocking. A YouTube video that emerged a month ago sparked talk of a child hit man — said by some to be as young as 12.

"I participated in four executions, but I did it drugged and under threat that if I didn't, they would kill me," the boy said calmly when he was handed over to the federal prosecutor Friday morning, showing no remorse.

Authorities identified the curly-haired suspect by his first name only — Edgar.

He told reporters early Friday he was kidnapped at the age of 11 and forced to work for the Cartel of the South Pacific, a branch of the splintered Beltran Leyva gang, and that he had participated in at least four decapitations.

Authorities said the siblings were detained at an airport near Cuernavaca in Morelos state with paid tickets to flee the country.

Morelos Gov. Marco Adame Castillo said the boy was born in San Diego, California, and Mexican officials were researching whether he has dual nationality. A U.S. Embassy official who spoke on condition of anonymity due to embassy policy said American officials had not yet confirmed his citizenship.

The boy's sister said they were headed for Tijuana, where they planned to cross the border and seek refuge with their stepmother in San Diego. Their mother sent them money for the tickets, she said, but it was not clear where their parents are.

The army did not say whether the children had passed security when they were detained. Neither has been formally charged.

The two allegedly worked for Julio "El Negro" Padilla, who has been fighting for control of the drug trade in Morelos, formerly part of the territory under the Beltran Leyva gang, which broke up with the killing of leader Arturo Beltran Leyva by Mexican marines a year ago. The battle among remnants of the gang has caused an unprecedented spike in violence in Morelos and in neighboring Guerrero state, where the resort city of Acapulco is located.

El Ponchis' sister said she was the girlfriend of Padilla and part of a group of girls called Las Chabelas, who helped dump bodies on streets and freeways in and around Cuernavaca, a city about 56 miles (90 kilometers) south of Mexico City. She said her brother introduced them.

An adult sister picked up at the airport appeared with the two Friday, but authorities said she has no ties to drug trafficking.

Stories of a hit boy, maybe as young as 12, spread after a YouTube video appeared last month with teens mugging for the camera next to corpses and guns. One boy on the video alleged that "El Ponchis" was his accomplice. State and federal authorities refused to confirm El Ponchis even existed.

In the video, the youth told an unseen questioner that his gang was paid $3,000 per killing.

"When we don't find the rivals, we kill innocent people, maybe a construction worker or a taxi driver," the youth is heard saying.

Figures obtained by The Associated Press from Mexico's attorney general's office show that the number of youths 18 and under detained for drug-related crimes has climbed steadily since President Felipe Calderon launched his assault on cartels in 2006. There were 482 that year and 810 in 2009. There were 562 in the first eight months of this year, on track to surpass last year.

Calderon has acknowledged that "in the most violent areas of the country, there is an unending recruitment of young people without hope, without opportunities."

The federal government has said the cartels are recruiting ever younger assassins to replace those killed or arrested in the current wars among the gangs and with the government. The government also has said that cartels prefer underage youths because they shorter sentences if caught.

Unlike the United States, Mexico has no system for trying juveniles as adults, though a bill that would establish such a provision is before the Mexican Senate. In Mexico, juveniles are sentenced to youth detention centers and are freed at age 18.

Although state courts handle crimes by juveniles in Mexico, authorities in Morelos have asked Mexico's federal government to take over the case because of the gravity of the crimes.

Neighbours said the siblings were living in a cartel safehouse in a poor neighborhood of Jiutepec, a working-class suburb of Cuernavaca. The area has an industrial area with Nissan, Unilever and other factories, rustic single-level concrete homes and some farms.