A NASCAR driver in the United States has alleged that his ex-girlfriend is a "trained assassin".

Kurt Busch, known as 'The Outlaw', told a court of his claims that Patricia Driscoll has taken part in many covert missions around the globe.

He says she once left the house in camouflage gear, only to return home later with a dressing gown splattered in blood.

"Everybody on the outside can tell me I'm crazy, but I lived on the inside and saw it firsthand," he said.

Busch is in court contesting a protective order that Driscoll has served against him. She describes the claims as "ludicrous" and said he had based them on a film script she is writing and that he proofread.

Driscoll has also filed a separate criminal complaint against Busch, which alleges that he slammed her head into a wall.