The U.S. State Department is investigating an allegation that an employee of the American Embassy in Mexico City passed sensitive information to a major drug cartel.

The report stems from a scandal at the organized crime unit of the Mexican attorney general's office, where 35 employees were accused yesterday of passing information about investigations to the Beltran-Leyva narcotics organization. The informants collected as much as $450,000 a month, The Associated Press reported.

A unnamed protected witness (who The New York Times said went by the alias "Felipe") also told authorities that he spied for the drug cartel on U.S. Drug Enforcement Administration agents while working as a criminal investigator at the U.S. embassy, according to El Universal, a Mexico City newspaper.

DEA intelligence chief Anthony Placido said at a Washington news conference today that he was concerned about Felipe's claims, but said he couldn't confirm that embassy information about drug-enforcement measures had been passed on to drug lords.

The revelations mark the "most serious known infiltration of anti-crime agencies" in Mexico since the 1997 arrest of Gen. Jesus Gutierrez Rebollo, then the country's top anti-drug chief. He is now serving 71 years in prison.

El Universal reported Monday that the alleged spy might have revealed details about the U.S. hunt for American drug suspect Craig Petties, who was captured in January after five years on the run. Petties has been accused of operating a multimillion-dollar marijuana and cocaine ring that stretched from Mexico to Texas, Mississippi and Memphis.