The documents said an estimated 60 Afghan and Iraqi terrorists were planning with the help of Mexican drug cartels to sneak into the United States through underground tunnels and attack the base, the largest intelligence-training center in the country, with high-powered weapons, The Washington Times reported Monday.

"A portion of the operatives were in the United States, with the remainder not yet in the United States," said one of the documents, a Federal Bureau of Investigation advisory that was circulated among law enforcement agencies. "The Afghanis and Iraqis shaved their beards so as not to appear to be Middle Easterners."

Lt. Col. Matthew Garner, spokesman for Fort Huachuca, said details of the investigation and the security changes made after the threat came to light in May "will not be disclosed."

"We are always taking precautions to ensure that soldiers, family members and civilians that work and live on Fort Huachuca are safe," Garner said. "With this specific threat, we did change some aspects of our security that we did have in place."