The son of a Tennessee state lawmaker has pleaded not guilty to hacking the email account of Republican vice-presidential candidate Sarah Palin.

David Kernell, 20, of Knoxville, Tennessee, entered the plea in federal court in Knoxville, on Wednesday, the same day prosecutors unsealed an indictment charging him with intentionally accessing Mrs Palin's email account without authorisation.

Kernell, an economics student at the University of Tennessee, was brought into court wearing handcuffs and shackles on his ankles.