European airports have begun to enforce stricter security measures amid US concerns that al Qaeda terrorists are developing explosives which could be smuggled onto planes.

Officials in Frankfurt have adopted tighter regulations, as has the UK, where authorities say the latest measures are likely to remain in place permanently.

Philip Baum, Editor of Aviation Security International explained the new procedures.

“This will mean an increase in the number of secondary searches, the increase in the number of people that might be asked to remove shoes if they’re going on certain flights. And greater scrutiny of passengers boarding certain flights, particularly those to the United States,” he said.

Legally, Washington has the authority to enforce the new requirements on foreign governments if the flights go directly to the US.

The United States Department of Homeland Security did not specify what has triggered the extra precautions.