(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 can'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 don'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.