Washington is promising an urgent air security review amid growing questions about the case of a Nigerian man charged with trying to blow up a transatlantic flight.
Airport screening around the world has already been stepped up and there are some reports of in-flight restrictions being introduced, including controls on restroom access.
Authorities are investigating whether Al Qaeda recruited Umar Farouk Abdulmutallab, who is charged with trying to ignite explosives on a flight between Amsterdam and Detroit on Christmas Day.
The US Homeland Security Secretary says officials did not have enough information to put the British-educated man on a so-called “no fly” list.
It has emerged that Abdulmutallab’s father reported him missing in November, voicing concerns about his behaviour.
His name was added to the least urgent of three lists of people monitored by the authorities. But he was not considered to be high-risk enough to be on the list of people banned from travelling on planes.
Abdulmutallab has reportedly told US authorities that he met militants in Yemen and they gave him the explosive device.