US military unveils heat-ray gun

The prototype weapon - called Silent Guardian - was demonstrated at the Moody Air Force Base in Georgia.A beam was fired from a large rectangular dish mounted on a Humvee vehicle.

The beam has a reach of up to 500 metres (550 yards), much further than existing non-lethal weapons like rubber bullets.

It can penetrate clothes, suddenly heating up the skin of anyone in its path to 50C.

But it penetrates the skin only to a tiny depth - enough to cause discomfort but no lasting harm, according to the military.

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.