U.S. security authorities are warning that terrorists may try to smuggle explosives onto airplanes by having them surgically implanted in their bodies.

News emerged Wednesday that the U.S. Department of Homeland Security last week advised its foreign counterparts that it has intelligence indicating renewed interest in the technique.

The reports did not indicate the source of the new intelligence. But a spokesman for the Transportation Security Administration, Nick Kimball, told reporters that air travelers may experience additional screening at airports because of the new threat. He said such measures could include more interaction with passengers, pat-downs, and the use of “enhanced tools and technologies.”

He said the techniques are designed to be unpredictable, so passengers should not expect to see the same methods used at every airport.

CNN reports that full-body scanners cannot detect items implanted in bodies.

In the past, terrorists have tried smuggling explosives aboard planes in shoes, clothing, and luggage. A Nigerian man was arrested in 2009 after attempting to ignite explosives in his underwear on a flight from Amsterdam to Detroit.