Mexico City (CNN) -- A 14-year-old accused of ruthless killings on behalf of a Mexican drug cartel boss is a U.S. citizen, a U.S. State Department spokeswoman said Monday.





Gini Staab would not provide any further information.





"We have confirmed the boy's U.S. citizenship but can't say  anything more about the boy's situation in the absence of a (provisional arrest warrant) signed by at  least one of the parents," Staab said.





Earlier, Staab said that the boy, once his citizenship was confirmed, would be given "all appropriate consular assistance, just like we would for any U.S. citizen arrested and incarcerated overseas." Assistance would include prison visits, information on local attorneys and checks on his welfare, she said.





The teen -- reportedly carrying a birth certificate issued in San Diego  -- and two of his sisters were detained Thursday at an airport in central Mexico after an anonymous tip alerted authorities he was heading to Tijuana, Mexico, local media reported.





A spokeswoman for the Mexican attorney general's office said authorities detained the 14-year-old Thursday evening on suspicion of working as a drug-cartel hit man, but declined to provide details.





But the boy faced a battery of questions from reporters after he was detained, answering questions point-blank as camera flashes lit his face.





"I slit their throats," he said, describing what he said was the killing of four people.





The teen told reporters after his capture Thursday night that he was an orphan who joined the Pacifico Sur drug cartel when he was 12. He said Julio "El Negro" Padilla, one of the group's alleged leaders, threatened him.





"I either work or he'll kill me," the 14-year-old said.





With his hands shoved into the pockets of his cargo pants, the 14-year-old told reporters that he was paid weekly in dollars and pesos. But in answering questions about whether he knew what he was doing when he allegedly participated in the killings, the teen said he was under the influence of drugs and unaware of his actions.





"No, I didn't know," he said.





Troops standing beside the teen while the youth was interviewed wore masks to hide their faces -- a common sight in Mexico, where clashes between authorities and cartels have intensified since President Felipe Calderon announced a crackdown shortly after he took office in 2006.





But the teen's face was clearly visible.





Martin Perez, director of Mexico's Children's Rights Network, said late Friday that authorities should not have given television cameras and newspaper photographers access to the 14-year-old.





"It was completely inappropriate, the form of presenting him in front of the media," he said.





"Everyone has the right to be presumed innocent," he said. "Also, it could put his life at serious risk. We have to remember that this is a fight between criminal organizations."





CNN's Claudia Dominguez, Rey Rodriguez, Nick Valencia and Krupskaia Alis contributed to this report.
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