(NewsNation) — Mexican drug cartels have been illicitly transporting a wide array of military-grade weaponry from the United States with the assistance of American citizens, a CBS Reports investigation uncovered.

Documents and interviews, with current and former officials, obtained by the outlet revealed that the U.S. government has been aware of this for years.

However, sources told CBS the government has done little to stop weapons trafficking networks, which move up to a million firearms across the border yearly.

According to U.S. intelligence sources, the cartel networks pay Americans to purchase weapons from gun stores and online dealers across the U.S.

When CBS News asked the U.S. Department of Justice about its findings, an official said, “We absolutely recognize the problem here that … the lion’s share of firearms trafficked to Mexican cartels are coming from the United States.” 

For years, the U.S. has fought an unsuccessful battle against drug traffickers, who are currently fueling a deadly fentanyl epidemic.

Read CBS Reports’ full story here.