The U.S. Treasury Department sanctioned three Mexican citizens Wednesday — including a fugitive dubbed "The Anthrax Monkey" — for alleged involvement in the production and trafficking of the powerful synthetic opioid fentanyl.

It was the second round of sanctions in as many months against leading fentanyl traffickers from what federal officials called the "notoriously violent" Sinaloa drug cartel.

The three men sanctioned all worked in the violent border city of Tijuana. They allegedly moved large amounts of synthetic opioid fentanyl into the United States. The sanctions block any assets the targets may have in the United States and prohibit U.S. citizens from having any dealings with them.

The Treasury Department said two of the men, Alfonso Arzate Garcia and his brother, Rene Arzate Garcia, acted as "plaza bosses" for the Sinaloa Cartel in Tijuana. The brothers, who remain at large, are involved in carrying out kidnappings and executions for the cartel, officials said. 

The other is Rafael Guadalupe Felix Nuñez, "El Changuito Antrax," or "The Anthrax Monkey." He began his career as a hitman in the early 2000s and later joined a gang of hitmen, all of whom adopted "Anthrax" as their last names.

Apprehended in 2014, he broke out of prison in 2017.

"Since his escape from prison, Felix Nuñez has evolved into a powerful and violent Sinaloa Cartel leader in the city of Manzanillo, Colima, Mexico," the Treasury Department wrote in a news release.

In July, the Treasury Department sanctioned 10 Mexican citizens, including a brother-in-law of former gang kingpin Joaquín "El Chapo" Guzmán, for alleged involvement in the production and trafficking of fentanyl.

In April, three of Guzman's sons were among 28 Sinaloa cartel members charged in a massive fentanyl-trafficking investigation. The three men — Ovidio Guzmán López, Jesús Alfredo Guzmán Salazar and Iván Archivaldo Guzmán Sálazar, known as the Chapitos, or little Chapos — and their cartel associates used corkscrews, electrocution and hot chiles to torture their rivals while some of their victims were "fed dead or alive to tigers," according to an indictment released by the U.S. Justice Department.

In:
• Sanctions
• Mexico
• Fentanyl
• Cartel