The United States is stepping up security screenings of US-bound flights from some Middle East airports as a precaution after the crash of a Russian airliner in Egypt.
Homeland Security Secretary Jeh Johnson on Friday said the United States also would review its assessments of certain foreign airports and offer them help with security, as well as take other measures "both seen and unseen."
It came amid growing evidence that the plane that crashed last Saturday in the Sinai, killing all 224 people on board, was brought down by an explosion.
Sources close to the investigation told AFP that information from the airliner's flight data and voice recorders "strongly favours" the theory that a bomb exploded on board the Airbus A321.
Russia halted flights to Egypt, while Britain scrambled to evacuate passengers in the Red Sea resort of Sharm-el-Sheikh after cancelling flights following the crash.
Johnson noted that the facts and circumstances surrounding the crash were still under investigation, although US President Barack Obama on Thursday acknowledged the "possibility that there was a bomb on board".
Johnson described the US actions as "interim, precautionary enhancements to aviation security with respect to commercial flights bound to the United States from certain foreign airports in the region".
He said expanded screenings would be applied to items on aircraft, airport assessments would be enhanced in conjunction with US international partners, and offers of help would be made to beef up aviation and airport security.
Johnson said they were designed to provide "an additional layer of security for the travelling public".
"At this time these security enhancements are intended only for certain foreign airports in the region," he said in a statement.