THE FBI has warned of a potential security threat from small aircraft – just days ahead of the tenth anniversary of the September 11 attacks.

Federal agents, and staff from the Department of Homeland Security, told AP that al-Qaeda had been recently considering ways of attacking the aviation sector, believing aircraft to have a greater impact than other forms of mass transit.

Politico said a five-page document circulated among law enforcement staff earlier this year had been treated as routine, but had underlined al-Qaeda’s alleged interest in recruiting Westerners to to be trained in flying small aircraft.

Now, however, the FBI and DHS have issued a nationwide alert about the threat of small planes being used for terrorist purposes, explaining that terrorist have considered renting planes and loading them with explosives.

CBS Local quoted NYPD police commissioner Ray Kelly who said there was no specific or credible threat, but that his department had stepped up its security protocols as a precaution.

“We of course are concerned, particularly because [Osama] bin Laden spoke about it twice in the notes that were recovered.”

A DHS spokesman told AP that the bulletin was “routine” and had been shared simply to highlight the need for continued vigilance.

CNN said the bulletin was issued on Friday, just nine days before the tenth anniversary of the attacks on the World Trade Center which killed almost 3,000 people.