A coordinated series of law enforcement raids across 16 states this week resulted in the arrests of 429 people accused of participating in smuggling and transportation networks for Mexican drug cartels, Attorney General Eric H. Holder Jr. announced Thursday. The raids, which took place Wednesday and involved more than 3,000 federal, state and local law enforcement officers, were a 'very significant blow' to the cartels' ability to move drugs across the border and distribute them in the United States -- and to smuggle cash and weapons into Mexico, Holder said. 'This interagency cross-border operation has been our most extensive, and most successful, law enforcement effort to date targeting these deadly cartels,' Holder said at a news conference. Officials seized $5.8 million in cash, 2,951 pounds of marijuana, 247 pounds of cocaine, 17 pounds of methamphetamine, 141 weapons and 85 vehicles. Those raids were part of a larger, 22-month effort called Project Deliverance, in which a series of related operations aimed at delivery networks resulted in some 2,200 total arrests and the seizure of 74.1 tons of illegal drugs, the Justice Department said. Michele M. Leonhart, the acting administrator of the federal Drug Enforcement Administration, said the effort had 'inflicted a series of blows that will have a real impact on the cartels and their ability to function.' She also said federal agents were seeing 'more sophisticated' ways of smuggling drugs across the border. In the past, she said, agents had seized drugs carried by individual passengers on commercial buses. But during this operation, drugs and money were found hidden within the structure of commercial buses. At a background briefing for reporters, another DEA official said some drug smugglers had developed ways to hide several pounds of drugs inside a car's transmission while still allowing the engine to function. He also described the alleged smugglers and distributors arrested in the sweeps as 'mercenary transportation groups' who worked for multiple cartels, rather than operating as arms of specific gangs. The official also said the operation was likely to disrupt the flow of drugs from Mexico for a period by removing the 'institutional memory' of figures who are experts in drug transportation. Holder also praised Mexican government officials as 'waging a courageous battle' against the violent drug cartels, singling out their arrest last month of Carlos Ramon Castro-Rocha, who has been indicted in the United States on charges of importing heroin. Holder rejected the notion that there may be mounting tension between law enforcement agencies in Mexico and the United States after the shooting death of a 14-year-old Mexican by U.S. border agents Monday. While expressing 'our sincere regrets about the loss of life for that 14-year-old youngster,' and saying that the FBI was investigating the incident, Holder said law enforcement officials on both sides of the border have an enduring 'bond' based on their interest in combating violent drug trafficking organizations. While praising the operation as a success, Holder and other officials said it would not stop drug smuggling from Mexico. 'Has drug trafficking come to an end? Of course not,' said John Morton, the head of Immigration and Customs Enforcement. 'But it just got harder and there are a lot of people this morning who wish they had a made a better career choice in life.' 