Washington, Apr 1 (IANS): US intelligence agencies have announced that terror groups have developed innovative ways to plant explosives in electronic devices that can evade some commonly used airport security screening methods, a media report said.

Heightening the concern is US intelligence suggesting that terrorists have obtained sophisticated airport security equipment to test how to effectively conceal explosives in laptops and other electronic devices, the CNN report said late Friday.

Through a series of tests conducted late last year, the Federal Bureau of Investigation (FBI) determined the laptop bombs would be far more difficult for airport screeners to detect than previous versions terrorist groups have produced.

The FBI testing focused on specific models of screening machines that are approved by the Transportation Security Administration and are used in the US and around the world, the report citing intelligence officials said.

"As a matter of policy, we do not publicly discuss specific intelligence information. However, evaluated intelligence indicates that terrorist groups continue to target commercial aviation, to include smuggling explosive devices in electronics," the Department of Homeland Security told CNN in a statement.

The US and European countries use a layered approach to security screening that goes beyond X-ray equipment, including the use of bomb-sniffing dogs and explosive-trace detection, according to American officials.

FBI experts have tested variants of the laptop bombs using different battery and explosive configurations to assess how difficult it would be for airport screeners to detect them.

The airline restriction, which took effect from March 21, bans many electronics from the cabins of planes flying directly to the US from airports in eight Muslim-majority countries, the report said.

Passengers on those flights must place electronic devices larger than cellphones in their checked luggage.

The ban was instigated after intelligence and law enforcement agencies determined that terrorists were working to place explosives inside laptop battery compartments in a way that would enable the devices to still power on in order to pass airport screenings.