The Mexican army has arrested a 14-year-old suspected drug cartel assassin who became infamous after photographs of him posing with guns, drugs and victims were posted online a few weeks ago.

Edgar Jimenez – nicknamed El Ponchis or "the cloak" – was detained as he prepared to board a plane in the central Mexican city of Cuernavaca bound for Tijuana, on the border with the US.

El Ponchis was accompanied by his two sisters, who allegedly also belonged to the gang and were responsible for disposing of the bodies of its victims, mostly dumping them by the roadside.

One of the sisters, 19-year-old Isabel, was preparing to travel with El Ponchis. She told reporters that once in Tijuana they planned to cross the border to San Diego in California where their mother lives and they are from.

It was not immediately clear whether they are US citizens.

Shortly after being arrested late on Thursday night, El Ponchis told reporters he had beheaded at least four victims who were found hanging from a bridge over the motorway linking Cuernavaca to the capital a few months ago.

The teenager said he regretted all the murders he had committed.

"I didn't join [the gang], I was pulled in," he reportedly said. "I got high on weed and didn't know what I was doing."

He said the leader of the gang, known as El Negro and reputedly the boyfriend of Isabel, began giving him drugs at the age of 12 and later ordered him to begin killing or be killed himself.

El Ponchis is a particularly disturbing example of the increasing number of very young people who are being pulled into the Mexican drug gangs and their violent wars against each other and the authorities.

His gang belonged to a branch of the Beltrán Leyva trafficking cartel which split into two after its leader, Arturo Beltrán Leyva, was killed one year ago at the end of a lengthy gun battle with navy special forces in an upmarket apartment complex in Cuernavaca.

Since then a series of high level arrests have all but destroyed the organisation that was once one of Mexico's most powerful trafficking cartels.