Distress signal

Washington (Reuter) - The symbols 'USA' carved in a Loatian rice field and once considered evidence that US prisoners were left behind after the Indochina war were made by a rice farmer's son, a US defence official said yesterday.

General James Clapper, appearing before a a Senate Select Committee, said US investigators had established that the boy carved a stick-figure aircraft and the letters 'USA' in the rice field, photographed by a US satellite in 1988, because he liked their shape.