Washington ? X-ray machines that screen airline passengers’ shoes cannot detect explosives, according to a Homeland Security Department report on aviation screening.

Findings from the report, obtained by The Associated Press, did not stop the Transportation Security Administration from announcing Sunday that all airline passengers must remove their shoes and run them through X-ray machines before boarding commercial aircraft.

The shoe-scanning requirement was ordered as the government fine-tunes new security procedures since British police last week broke up a terrorist plot to assemble and detonate bombs aboard as many as 10 airliners crossing the Atlantic Ocean from Britain to the United States.

Among the new procedures are a ban on liquids and gels in airline passenger cabins, more hand searches of carryon luggage, and random double screening of passengers at boarding gates.

On Sunday, the TSA made it mandatory for shoes to be run through X-ray machines as passengers go through metal detectors. They were begun in late 2001, after the arrest of Richard Reid aboard a trans-Atlantic flight when he tried to ignite an explosive device hidden in his shoe. The shoe scans have been optional for several years.

In its April 2005 report, “Systems Engineering Study of Civil Aviation Security – Phase I,” the Homeland Security Department concluded that images on X-ray machines don’t provide the information necessary to detect explosives.

Machines used at most airports to scan hand-held luggage, purses, briefcases and shoes have not been upgraded to detect explosives since the report was issued.

TSA spokeswoman Yolanda Clark said putting shoes on the X-ray machines makes the screening process more efficient and eliminates confusion. “We do not have a specific threat regarding shoes,” Clark said. “In an abundance of caution we require all shoes to be removed and X-rayed to mitigate a variety of threats.”

The Homeland Security report said that “even a 1/4-inch insole of sheet explosive” could create the kind of blast that reportedly brought down Pan Am flight 103, the airliner that blew up over Lockerbie, Scotland, in December 1988, killing 270 people in the air and on the ground.

“To help close this gap, the percentage of shoes subjected to explosives inspection should be significantly increased,” the report said.

The Homeland Security report recommends that explosives trace detection, or ETD, be used on the shoes and hands of passengers when the screeners determine they must be checked more thoroughly.

“Within the current state of the art, they afford the only meaningful explosives detection capability at the checkpoint,” the report said.