By Mark Hosenball
WASHINGTON, Feb 20 (Reuters) - The latest warning to airlines about shoe-bomb threats is a product of heightened U.S. concern about al-Qaeda's Yemen-based affiliate, whose leaders include a technically-savvy bombmaker, U.S. security sources said on Thursday.
U.S. Homeland Security authorities on Wednesday issued a new warning about shoe bombs to airlines which fly from overseas to the United States out of concern that Ibrahim Hassan al-Asiri, a Saudi believed to have been behind failed plots to attack airliners with explosives hidden in shoes or clothing, may have come up with new bomb design innovations to evade airport security measures, the sources said.
The sources said the warnings were sent to airlines flying to the U.S. from around thirty airports in Europe, the Middle East and Africa.
Among European airports where airlines were requested to take extra security precautions about possible shoe bombs are Amsterdam's Schiphol, London's Heathrow and Gatwick, and the airport in Manchester, England, the sources said.
The warning is not related to the Winter Olympics in Sochi, Russia. It applies to airlines operating flights from specific foreign airports to U.S. airports, rather than domestic U.S. flights or flights outbound from the U.S. to foreign destinations, security sources said.
The security warning, sent to both U.S. and foreign carriers flying such routes, includes instructions for the types of enhanced security checks that should be undertaken, including detailed recommendations regarding how to search female passengers, the sources said.
The sources attributed the latest warning to recent intelligence that points to possible increased threats posed by devices produced by al-Qaeda in the Arabian Peninsula, a Yemen-based affiliate of al-Qaeda's central organization whose leading members include both Yemeni and Saudi militants.
Alleged bomb-maker Asiri has been described by security officials as one of the most dangerous and innovative explosives experts ever to join the al-Qaeda network.
Believed to be in his early 30s, Asiri became a high priority for Western spy agencies following his alleged role in planning airliner-related attacks on the United States in 2009 and 2010.
One such plot was a failed bombing of an airliner over Detroit on Christmas Day in 2009 by a Nigerian militant who had an explosive charge built into his underpants. Asiri reportedly was wounded in a U.S. drone attack last year.
The security sources said the latest warning did not mean that the United States had intelligence indicating a specific shoe bomb plot was in progress.
It is consistent with concerns security agencies have about militants trying to smuggle explosives onto airplanes in shoes, cosmetics or liquids. Earlier this month, U.S. authorities advised airlines flying to Russia for the Sochi Winter Olympics to watch out for toothpaste tubes that could hold bomb-making ingredients and could be smuggled through airport security checkpoints. (Additional reporting by Warren Strobel; Editing by Alistair Bell and Chris Reese)