Loopholes still exist in U.S. airport security for terrorists smuggling liquid explosives and detonators, a report by the U.S. Government Accountability Office (GAO) stated on Nov. 14.

According to investigations by the GAO, known as "the investigative arm of Congress," liquid explosives and detonators were successfully smuggled by undercover GAO investigators through some U.S. airport security checkpoints.

"Our tests clearly demonstrate that a terrorist group, using publicly available information and few resources, could cause severe damage to an airplane and threaten the safety of passengers by bringing prohibited IED (improvised explosive device) components through security checkpoints," the report said.

During the tests conducted at 19 U.S. airports in March, May and June this year, the GAO investigators managed to pass the Transportation Security Administration (TSA) checkpoints carrying components to make the IED.

Two investigators even concealed the materials in their carry-on luggage and on their person, the report said.

The components for IED are available for less than US$150 at local stores and over the Internet, the report added.

However, TSA refuted the GAO's report, saying the investigators only tested one of the TSA's 19 layers of security at airports.

"While people think about us in terms of the checkpoints and they see us as the checkpoints, there's a lot more layers of security," TSA spokeswoman Ellen Howe said.

TSA updated its security measures in August 2006 after British authorities foiled a plot to use liquid explosives to attack U.S.-bound airplanes.

Apart from the checkpoints, TSA's security measures include checking the validity of documents and observing people's behavior throughout the airport.

"Just because somebody gets through one layer doesn't mean they're going to get through all of the layers," Howe added.

However, TSA accepted the GAO's recommendation that airports should adopt "more aggressive, visible and unpredictable security measures," as well as new detection technologies.