But Embassy spokesman Alexander Featherstone said his citizenship has not been determined and U.S. officials met with the teen on Monday to offer him consular assistance "in case he is a U.S. citizen."

The boy, who authorities only named publicly as Edgar, was arrested Thursday with a 19-year-old sister, Elizabeth Jimenez Lugo, as they tried to board a plane to Tijuana in an airport near Cuernavaca south of Mexico City. The two planned to cross the border into San Diego to be with their mother, Jimenez Lugo told reporters when they were handed over to federal authorities on Friday. Soldiers also detained their sister, Lina Erika Jimenez Lugo, 23, who had driven them to the airport.

No birth certificate for the boy is on file in San Diego County. But birth records show Elizabeth Jimenez Lugo was born in 1991 at Mercy Hospital and Medical Center in San Diego and her sister, Lina Erika, is registered as having been born in Juitepec, Mexico. Both records show Carmen Solis, their paternal grandmother, was listed as their mother but no father is shown on either birth certificate.

Officials say Edgar worked for the Cartel of the South Pacific, a branch of the splintered Beltran Leyva gang fighting for control of the central state of Morelos, where he grew up.

Mexico's Organized Crime Unit said late Monday it is holding the boy's sisters for 30 days for investigation of possible kidnapping and organized crime charges.

Soldiers hunting for Mexico's alleged child assassin barged into a baptism party of the 14-year-old suspect's young cousin in late November to search every corner. They returned two days later, nearly breaking down the gate to the two-story concrete house shared by several families in a working-class suburb of Cuernavaca.

This time they even checked under the bed, but didn't find the boy.

After that, his family decided to send him with his sister to San Diego to be with their mother, a close relative told The Associated Press under condition that his name not be used for fear of retaliation.

"We didn't think he would get caught," he said.

Both authorities and alleged cartel members call him "El Ponchis," but the relative said his nickname is "Ponchi," a name the family gave him when he was a pudgy 4-year-old.

The boy told reporters that he was kidnapped and forced to work for the cartel at age 11 and participated in at least four executions, though he said he was drugged and under threat.

When he was still a baby, Edgar's father brought the boy with five siblings from San Diego back to Jiutepec, an industrial suburb of Cuernavaca, to live with the father's mother, Carmen Solis, who raised them until she died, the relative said, though he didn't say when she died.

"The boy loved her very much, and we watched how he would hug her as if she were his mother," the relative said.

Neighbors said the father remarried and the two captured teens talked about a stepmother.

Authorities say he and his sister 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 19-year-old girl was allegedly Padilla's girlfriend.

The family knew the petite boy with curly hair and soft voice was hanging out with the wrong crowd but refuse to believe he was a killer for hire.

Ponchi was an errand boy, not an assassin, the relative said of the boy, who allegedly appears in several videos on the Internet showing teenagers claiming they were drug cartel assassins. Some said he was as young as 12.

"He is a sweet boy," the relative said. "Maybe he appeared in the video just to show off."

**Associated Press writers Elliot Spagat in San Diego and Olga R. Rodriguez in Mexico City contributed to this report.