( CNN ) -- Allegations surrounding a U.S. investigation that may have involved laundering money for Mexican drug cartels are causing concern on both sides of the border . In Mexico , lawmakers say they are furious and are demanding an investigation . In the United States , a congressman is broadening the oversight of a previous inquiry to include the most recent allegations . Felipe Gonzalez , a federal senator with Mexico 's ruling PAN party , says they will demand an investigation to determine whether the U.S. Drug Enforcement Administration allowed its agents to launder money , possibly even on Mexican soil , as part of an investigation into the inner workings of Mexican drug cartels . Gonzalez called the situation `` really , really bad '' and said that `` this is not increasing the trust among countries to work together against crime . Furthermore , you ca n't fight crime by committing criminal acts and violating the law . '' Last weekend , the New York Times reported that DEA agents `` have handled shipments of hundreds of thousands of dollars in illegal cash across borders . '' Rep. Darrell Issa , R-California , announced Monday an investigation into the allegations in his role as chairman of the House Oversight and Government Reform Committee . In a letter to U.S. Attorney General Eric Holder , Issa said , `` These allegations , if true , raise further unsettling questions about a Department of Justice component engaging in a high-risk strategy with scant evidence of success . '' Furthermore , Issa wrote that the existence of such a program again calls Holder 's leadership into question . Tensions stemming from law enforcement actions have long troubled relations between Mexico and the United States . Samuel Gonzalez , a security analyst in Mexico City , says Mexicans are especially sensitive when it comes to their territory . `` Of course there 's a jurisdiction problem and , in the end , maybe a violation of sovereignty . That has to be determined and find out where the operations were carried out , '' Gonzalez said . Robert Strang , a former DEA agent , says infiltration of Mexican drug cartels is not only happening , but it 's essential in investigations aimed at dismantling Mexican criminal organizations by targeting their finances . `` There 's only one way really to catch these major drug cartels , the leaders of these cartels , and that 's to follow the money , because these leaders do n't go anywhere near the drugs themselves . They hire people to do that , '' Strang said . As an answer to he allegations published by The Times , the DEA issued a statement Tuesday saying , `` We do not discuss the operational aspects of law enforcement activities . '' The statement also said that the DEA has been `` working collaboratively with the Mexican government to fight money laundering for years . As a result of this cooperation , we have seized illicit transnational criminal organization money all around the world through our partnership with law enforcement . '' For Strang , the former DEA agent , the bottom line is whether these actions produce results . `` The real question here is whether or not undercover agents need to sell drugs , buy drugs , and launder money . And I 've got to tell you , there 's no way to make these kinds of great international , sophisticated conspiracy cases unless you 're going to do that , '' he said . Last month , a small group of Mexican legislators requested the extradition of American agents involved in Operation Fast and Furious . This operation , run by the Bureau of Alcohol , Tobacco , Firearms and Explosives , allowed the illegal smuggling of firearms from the United States into Mexico in an effort to learn about smugglers . Many weapons were lost and likely ended up in criminal hands . U.S. Attorney General Eric Holder is expected to answer key questions about Operation Fast and Furious as he appears Thursday before a congressional panel including Issa , who also is leading the congressional investigation into the flawed gun sting program .
Mexican and U.S. lawmakers called for investigations . Allegations that the FBI used agents to steal money , perhaps even on Mexican soil . Mexican Sen. Felipe Gonzalez : ` ` You ca n't fight crime by committing criminal acts '' A former DEA agent says infiltration of Mexican drug cartels is essential .