The U.S. government has reportedly launched a pair of probes to determine whether Afghan officials have been using military planes - much of which paid for by the U.S. - to illegally smuggle guns and drugs around the country.

According to a report by The Wall Street Journal, both the U.S. Drug Enforcement Agency and the U.S.-led coalition forces in Afghanistan are separately investigating suspected illicit activities carried out under the noses of U.S. military advisers and possibly with the knowledge of high Afghan officials.

Suspicions about alleged corruption in the Afghan Air Force (AAF) were disclosed publicly in January in a U.S. Air Force special investigation report on the murder of eight U.S. Air Force personnel and one contractor by an Afghan officer who later turned his gun on himself in the Kabul airport in April 2011. The shooter in that case was identified as Col. Ahmed Gul, a cargo and passenger coordinator for the AAF with reported financial and mental problems.

In the Air Force report, two witnesses stated they believed the AAF to be a hotbed of "nefarious" activity where Afghan officials could make quick money by ferrying people or cargo around the country - often with little or no screening.

"There is a distinct lack of transparency in the way the Afghan Ministry of Defense [and the] AAF like to schedule and fly their missions," one witness, only identified as a Lieutenant Colonel, says in the report. "The Afghans either don't know or don't want to tell us who or what they're flying around the country. All this looks very suspicious to the NATO Air Training Command-Afghanistan mentors who have been in country for more than a few months."

Specifically, the witnesses said the Afghan air officers would be paid directly to usher top Afghan officials around at the last minute. In its report today, The Wall Street Journal quoted U.S. Army Lt. Gen. Daniel Bolger as saying the current allegations also include the transport of narcotics and weapons "for the use of private groups" within Afghanistan. The United Nations estimates that Afghanistan is home to 90 percent of the world's opium - the main ingredient in heroin.

Though the Air Force investigation did not find a singular motive for Gul's sudden attack, when the shooting took place a new system "was being developed to ensure [AAF] flights were officially tasked through a legitimate [AAF] process…" the Air Force report said.

In a statement to ABC News, the U.S.-led International Security Assistance Force said today it is working with its Afghan partners to "arrest and reverse criminal penetration in the [Afghan National Security Forces] and to ensure security ministries and their forces become sufficiently resistant to and insulated from criminal network interference and subversion."

"ISAF takes seriously any allegation of impropriety on the part of its forces or those of the Afghan National Security Forces we mentor and partner with," the statement said. The statement noted that in the last year, 50 "criminal actors" had been discovered in the security forces.

A DEA spokesperson told ABC News that by policy, the administration does not confirm or deny any potential ongoing investigations. A spokesperson for the AAF and Afghanistan's Minister of Defense, Gen. Abdul Rahim Wardak, told The Wall Street Journal they were unaware of the investigations. The AAF spokesperson denied the allegations.

READ WSJ: Afghan Air Force Probed in Drug Running