The plot was like something from a Hollywood blockbuster: dozens of foreign terrorists working with a Mexican drug cartel to attack a Southern Arizona Army post with anti-tank missiles and grenade launchers.

Paying one of Mexico's most ruthless drug cartels $20,000 apiece, 60 Afghan and Iraqi terrorists would be smuggled into Texas and hole up at a safe house.

Their weapons, Soviet-made and easily acquired on the black market, were funneled through Arizona and New Mexico in hand-dug tunnels that cut across the border.

Their target: 13,500 military personnel and civilians working at Fort Huachuca, roughly 75 miles southeast of Tucson.

But the plot, widely reported by local stations and national TV networks and The Washington Times, turned out to be nothing more than fiction, an FBI spokesman said Monday.

"A thorough investigation was conducted, and there is no evidence showing that the threat was credible," said Manuel Johnson, an FBI spokesman based in Phoenix.

Experts earlier in the day expressed skepticism about the intelligence, which said the terrorists — who would shave their beards to fit in — planned to strike last May.

The group purchased anti-tank missiles, rocket-propelled grenades, rifles and handguns and was working with the Gulf Cartel to get into the United States, according to an account in the Times, which cited confidential law enforcement documents it had obtained.

The advisory, which was passed to Fort Huachuca commanders, caused the post to alter its security, though officials wouldn't say what they did.

Details of potential terrorist attacks against military installations routinely surface, post officials and intelligence experts said.

"As often as the FBI receives reports, they pass them along to us," said Lt. Col. Matthew L. Garner, a post spokesman.

He said he didn't know if post officials were skeptical of the intelligence but said all threats are taken seriously.

Officials at the post, less than a dozen miles from the Mexican border, routinely arrest illegal entrants on fort property, usually after they come up through the Huachuca Mountains.

In the last fiscal year, which ended in October, post officials caught 961 illegal entrants, according to records kept by Fort Huachuca military police. Of those, 684 were of Mexican descent while 277 came from elsewhere — though a further breakdown wasn't available.

Retired Maj. Gen. James "Spider" Marks, who served as a senior intelligence officer during the invasion of Iraq and commanded Fort Huachuca's intelligence program from 2001 to 2004, said military installations routinely receive intelligence saying they're potential targets.

While he hadn't seen the reports cited by the Times, Marks said that, in general, it's crucial to always question the validity of the sources involved.

The intelligence about the Fort Huachuca plot came secondhand from Drug Enforcement Administration sources in Mexico who were "of uncertain reliability," the Times reported.

"It's unfortunate that you have to assess credibility of intelligence after the fact," said Marks, who now runs a private intelligence-contracting business in Virginia.

Another intelligence expert questioned the timing of the leaked documents that detailed the plot, especially considering their release came some six months after the attack was supposed to have taken place.

"The timing is interesting," said Stephen Flanagan, director of the international security program at the Washington, D.C.-based Center for Strategic and International Studies, a think tank that specializes in security and economic policy. "On the other hand, these plots take time to unfold."

Even though unfounded, the plot speaks to the continued threat of weapons, drugs and possibly even terrorists coming across the border, he said.

"I think it's a general reminder that any military institution in the United States needs to be wary," he said. "The fact is, we know that the terrorist groups are always looking for a weak link in some chain."

● Contact reporter Aaron Mackey at 573-4138 or at