Criminal charges were filed on Wednesday against two former JP Morgan traders who were at the centre of a series of bad bets that cost the nation's largest bank more than $6 billion in losses.

US prosecutors charged Javier Martin-Artajo, a Spaniard who was in charge of the team that made the giant wagers in corporate credit investments that piled up losses early in 2012, and Julien Grout, a Frenchman who was responsible for recording and distributing daily values on the positions.