The FBI confirmed it has issued an "intelligence information report" warning of possible Al Qaeda attacks on Los Angeles and Chicago shopping malls over the holiday season.

The warning states Al Qaeda has been planning the attack for the past two years with the intension to disrupt the U.S. economy, but it notes the latest threats fit a pattern that has emerged every holiday season since the Sept. 11, 2001 terror attacks.

FBI officials say details of the threat have come from a reliable source, but said much of the information is second- and third-hand, leaving FBI officials uncertain about the reliability of the intelligence received.

"This information was obtained through a lengthy chain of acquisition, and was provided to the source by a sub-source who spoke in confidence. The veracity of the information is uncertain but the threat is being reported due to the nature of the information," the FBI said in a statement.

"In the post 9/11 era, sharing information is our top priority. Al Qaeda messaging has clearly stated they intend to attack the U.S. or its interests; however, there is no information to state this is a credible threat. We remind people to remain vigilant and report suspicious activity to authorities," added FBI Special Agent Richard Kolko.

Unclassified threat information was circulated by the FBI on Nov. 7, and is based on intelligence received in late September, according to ABC, which was first to report the story Thursday. The threat states that Al Qaeda has "been planning the attack for the past two years."

FBI sources say they are not "that worried" right now, but are operating under an "abundance of caution." Kolko indicated some annoyance that the information had reached the press.

"Portions of an FBI document, called an IIR (Intelligence Information Report) were leaked to the media. This document was intended for law enforcement and intelligence community partners for situational awareness," he said.