MCALLEN, Texas - A man arrested on federal drug and immigration charges in South Texas is believed to be the nephew of the former boss of Mexico's Gulf cartel and was a rising player in the drug trafficking network, a U.S. law enforcement official said Wednesday.

Rafael Cardenas Vela was arrested last week following a traffic stop in Port Isabel, a Gulf coast town that sits across the causeway from South Padre Island. He is charged with conspiracy to possess and distribute drugs and using a fraudulent passport, according to federal court records.

The law enforcement official familiar with the case told The Associated Press on Wednesday that authorities believe Cardenas Vela is the nephew of Osiel Cardenas Guillen and was a rising player in the cartel's operations. The official spoke on condition of anonymity because the person wasn't authorized to speak publicly about the case.

Cardenas Guillen was extradited to the U.S. in 2006 from Mexico and sentenced to 25 years in prison last year.

Angela Dodge, a spokeswoman for the U.S. attorney's office in Houston, said in an email that "we understand there is a familial relationship," but declined to comment beyond that.

A message seeking comment was left for Cardenas Vela's attorney.

The Gulf cartel is based in Matamoros, Mexico, across the border from Brownsville, Texas. Its territory is not what it once was, but it holds on to major drug smuggling corridors between Reynosa and Matamoros. Under Cardenas Guillen's leadership, the Gulf cartel spawned the Zetas, which started as the cartel's paramilitary muscle and evolved into a ruthless rival in their own right.

Port Isabel police said in a statement about Cardenas Vela's arrest that officers pulled over a silver Ford F-150 pickup with temporary Texas tags for speeding just after 6:30 p.m. Oct. 20. The truck was eastbound and just a short distance from the causeway that crosses to South Padre Island.

The driver was German Alejandro Huizar Marroquin, 31, of Ciudad Victoria, Tamaulipas, who presented a Mexican driver's license. The front-seat passenger was Cardenas Vela, though he presented a Mexican passport for 37-year-old Pedro Gonzalez Garcia, of Tomatlan, Jalisco.

Francisco Javier Escalante Jimenez of Matamoros and another man from Brownsville were in the backseat.

The officer found discrepancies in the identification for three of the four and called U.S. Immigration and Customs Enforcement for assistance. The men were taken to the Port Isabel police station and turned over to ICE custody.

ICE confirmed Cardenas Vela's arrest and said the investigation was ongoing but offered no other details Wednesday.

According to court records unsealed this week, special agents from Homeland Security Investigations, a branch of ICE, interviewed Cardenas Vela after the traffic stop.

Cardenas Vela presented a valid Mexican passport and U.S. visa under the name Pedro Garcia Gonzalez, but the agents determined that was not his true identity. He then admitted he has been involved in the transportation and importation of marijuana and cocaine into the U.S. for several years, records state. He told agents that two years ago he sold about five tons of marijuana to people he knew would import it into the U.S.

Huizar Marroquin and Escalante Jimenez were charged with making false statements about Cardenas Vela's true identity and remain in federal custody. Messages seeking comment were left for their attorneys Wednesday.