The US military has been showing off its latest toy, a device that uses microwaves to make the enemy feel that they are on fire.

Dubbed the Active Denial System, the weapon sends out a blast of microwaves which heats up the skin's surface to 130 degrees Fahrenheit, but only penetrates to a depth of 1/64th of an inch.

In the demonstration 10 journalists received a blast from the device, which is designed to be used in crowd control.

"This is one of the key technologies for the future," Marine Colonel Kirk Hymes, director of the non-lethal weapons programme at Quantico, which helped develop the new weapon, told Associated Press.

"Non-lethal weapons are important for the escalation of force, especially in the environments our forces are operating in."

The test was carried out from a range of 500 yards and the participants said that the sensation was so strong they felt that their clothing was about to combust.

The system is not expected to be in wide use until 2010 but all sections of the military, and some civilian law enforcement bodies, have expressed an interest.

Airman Blaine Pernell, 22, of suburban New Orleans, said during the test that he could have used the system during his four tours in Iraq, where he manned watchtowers around a base near Kirkuk.

He said that Iraqis constantly pulled up and faked car problems so that they could scout out US forces.

"All we could do was watch them," he said, adding that the ray gun would have allowed the troops to disperse the Iraqis.

However, a 2004 Nato report on non-lethal weapons warned that "excessive power levels [in the device] can have serious consequences for human targets".

The power level used with the Active Denial System is not public knowledge and neither is the safety margin, i.e. the difference in exposure time between being effective in 'repelling' people and causing permanent damage to skin or eyes.

The safety margin is thought to be in the realm of seconds, meaning that exposure to the beam has to be short to avoid adverse effects.

It is stated in one of the experimental protocols that the level of exposure to the radiation emitted by the Active Denial System may be as much as 20 times more than the limit set in the relevant US Air Force Occupational Safety and Health Standard.