Air passengers won't be able to board many inbound flights to the United States if their mobile devices, particularly phones, are out of power, the Transportation Security Administration (TSA) announced Sunday.

The edict follows heightened concerns that terrorists from Europe, the Middle East, and Africa may be plotting to blow up an airliner, the agency said. Travelers from those regions with flights headed to the United States will be asked to power on their devices before boarding, the TSA said. The agency said it was especially singling out Apple's iPhones and Samsung's Galaxy phones.

"As the traveling public knows, all electronic devices are screened by security officers. During the security examination, officers may also ask that owners power up some devices, including cell phones. Powerless devices will not be permitted onboard the aircraft. The traveler may also undergo additional screening," the TSA announced. "TSA will continue to adjust security measures to ensure that travelers are guaranteed the highest levels of aviation security conducted as conveniently as possible."

The measures came days after Homeland Security Chief Jeh Johnson ordered the agency to formulate new rules because of heightened security fears. As Johnson put it: