US aviation remains vulnerable to attack and groups such as al Qaeda may try to target non-commercial planes and helicopters, a newspaper reported on Monday, citing a confidential government report.

The report by the FBI and the Department of Homeland Security says the aviation industry is a tempting target for acts of terrorism due to the spectacular nature of such attacks, the New York Times said.

Billions of dollars have been spent to bolster security following September 11, 2001.

Commercial airliners are likely to remain a target, but intelligence indicates al Qaeda may have discussed plans to hijack chartered planes, helicopters and other general aviation aircraft because they are less well-guarded, the newspaper said.

"As security measures improve at large commercial airports, terrorists may choose to rent or steal general aviation aircraft housed at small airports with little or no security," the Times quoted the report as saying.

Al Qaeda "has apparently considered the use of helicopters as an alternative to recruiting operatives for fixed-wing aircraft operations," the report said.

It said the manoeuvrability and "non-threatening appearance" of helicopters make them attractive for those seeking to conduct suicide attacks on landmarks or to spray toxins below.