Three of the most violent Mexican drug cartels have been added to the list of banned foreign "drug kingpins" by President Obama, in a move that allows the federal government to seize their assets, the Washington Post reported April 16.

Obama's move also allows the government to seek criminal penalties against U.S. firms or individuals that provide weapons, launder money or transport drugs or cash for the cartels. The targeted cartels -- Sinaloa, Los Zetas and La Familia Michoacana -- have assets estimated in the billions of dollars.

Kingpin designations have been powerful tools against Colombian drug cartels, said Julie Myers, a former Justice Department official. In some cases defendants agreed to plea deals to protect family assets. However, "if there's no assets [identified], it's an important symbolic gesture, but it's kind of an empty threat," Myers said. 

Mexico's President Jose Calderon has pressed for more U.S. involvement in helping to stem the flow of guns into his country. The Mexican government sees a "direct correlation" between a surge in the seizures of U.S. guns in Mexico and the 2004 expiration of a U.S. ban on assault weapons, said Arturo Sarukhan, the Mexican ambassador to the U.S.

"Most of the assault weapons are coming from the United States," Sarukhan said. "The key issue right now is, how can the United States help to shut down those guns and shut down that bulk cash that is providing the drug syndicates in Mexico with the wherewithal to corrupt, to bribe, to kill?"

The effort to curb the flow of guns entering Mexico from the U.S. has faced heavy obstacles, including limited resources, relatively open access to firearms in the U.S., and political opposition to tighter gun regulations.