(CNN) -- The nephew and protege of an imprisoned Mexican drug cartel kingpin was arrested Wednesday by federal agents in southern Texas, an official told CNN.
Rafael Cardenas Vela was detained by U.S. Customs and Border Protection in Port Isabel, according to a court affidavit filed by Homeland Security Investigations Special Agent Tomas Salazar.
"He is the nephew" of Osiel Cardenas Guillen, Cameron County Sheriff Omar Lucio told CNN. He said the suspect told an officer with the sheriff's office of his relationship with the former head of the Matamoros-based Gulf Cartel, who is serving a 25-year drug-trafficking sentence at the Supermax prison in Fremont County, Colorado.
Under Cardenas Guillen's leadership, the Gulf Cartel was responsible for smuggling thousands of kilograms of cocaine and marijuana into the United States, according to the FBI.
Cardenas Vela told agents he, too, had been involved in "the transportation and importation of marijuana and cocaine into the United States for several years," and admitted to having sold nearly five tons of marijuana two years ago to people he knew were taking it to the United States for further distribution, the criminal complaint said.
Cardenas Vela was arrested early Wednesday in a traffic stop, Cameron County Constable Horacio Zamora said.
Texas authorities said they believe Cardenas Vela wants to mimic his uncle's work.
A Mexican citizen, Cardenas Vela was arrested carrying a valid Mexican passport and valid U.S. visa under the name "Pedro Garcia Gonzalez." He admitted to federal agents that he was in the United States without legal documentation and was using the visa to travel, the criminal complaint said.
It was not clear where the suspect was being held. Cameron County officials said Cardenas Vela was not in their jail system and federal authorities did not disclose his whereabouts.
"We usually do not provide details as to location of those in detention," said Angela Dodge with the U.S. attorney's office in Houston, which has jurisdiction over southern Texas.
Cameron County is home to Brownsville, across the river from Matamoros.
A representative of the federal attorney general in Mexico City said the office was aware of the arrest, but had no immediate comment.