DHAKA: The Obama administration is stepping up security for some flights headed to the United States from Europe and the Middle East, reflecting heightened concern that terrorists are developing more sophisticated bombs designed to avoid airport screening.

Homeland Security Secretary Jeh Johnson said in a statement that he has directed the Transportation Security Administration to "implement enhanced security measures in the coming days" at selected overseas airports.

Specific steps or airports were not disclosed. A homeland security official said that TSA would work with airlines and security agencies overseas and that the changes will primarily focus on airports in Europe and the Middle East.

The effort does not involve changes to what travelers can take aboard flights. But passengers may see additional inspections of shoes and electronics, additional use of scanners designed to detect trace amounts of explosives, and another stage of screening at boarding gates, in some cases, the official said.

The measures do not involve U.S. domestic flights, and passengers could see changes as early as next week.

The changes came about based on new intelligence on terror groups trying to build new types of improvised explosives that are harder to detect, the official told CNN. There was no specific plot.

Since hardening cockpit doors and taking other measures after the 9/11 al Qaeda attacks, the U.S. aviation security focus has shifted primarily from hijackings to plastic and other explosives that can be carried aboard a plane or hidden in baggage.

BDST: 0930 HRS, JUL 03, 2014