The US military has given the first public display of what it says is a revolutionary heat-ray weapon to repel enemies or disperse hostile crowds.

Called the Active Denial System, it projects an invisible high energy beam that produces a sudden burning feeling.

Military officials, who say the gun is harmless, believe it could be used as a non-lethal way of making enemies surrender their weapons.

A Reuters journalist who volunteered to be shot with the beam described the sensation as similar to a blast from a very hot oven - too painful to bear without diving for cover.