American air travellers may have their hands swabbed more often as part of a stepped-up effort to screen passengers for explosives, an Obama administration official said Wednesday.

U.S. Transportation Security Administration officer Robert Howard signals an airline passenger forward at a security checkpoint at Seattle-Tacoma International Airport early in January. (Elaine Thompson/Associated Press)

Airports in the United States were told Wednesday that more passengers should be randomly screened for explosives before, during and after they go through metal detectors, the official said. The screening could include swabbing travellers' hands or their carry-on luggage to check for traces of explosives, said the official, who requested anonymity to speak about security plans.

The heightened screening follows a Christmas Day attack on a Detroit-bound airliner. A Nigerian man accused of being trained by al-Qaeda operatives has been charged with trying to blow up the plane with explosives hidden in his underwear.

Other security measures have been enhanced since the December attack. Heightened screening measures have been tested at five airports over the past month.

U.S. Transportation Security Administration spokeswoman Kristin Lee said the stepped-up screening is random and that travellers will not see the same procedures at all airports.

The Associated Press