Radio personality Howard Stern has criticised CBS chief Les Moonves -- and used airtime on Moonves' network to do so.

Appearing on David Letterman's Late Show, Stern called Moonves "one of the biggest jerks on the planet," adding: "He's a bully, Dave."

The ongoing feud between Stern and Moonves kicked off in 2004 when Stern announced he was moving to satellite radio -- a platform where free speech remains outside the reach of America's communications regulator -- and quitting CBS Radio. Last month, CBS filed a lawsuit claiming that Stern breached his contract with CBS by promoting his move to Sirius Satellite Radio between October 2004 and December 2005, when he left CBS. Moreover, the suit alleges that Stern's promotions for Sirius were part of a secret marketing plan.

"There was no secret agreement, there [were] no secret payouts," Stern said.