Lucas has had to re-think his marketing approach

The admission was reported by Newsweek, which had obtained a copy of a Lucasfilm merchandise marketing document.

The Phantom Menace still went on to earn nearly $1bn (�690m) around the world, making it the fourth-biggest grossing film ever released.

But the marketing document quoted by Newsweek appears to reveal Lucas' concerns about the film - and promises the new Star Wars adventure, Attack Of The Clones, will be an improvement.

The new film will have a "darker feel, closer to the original saga" and "no silly characters or kids", says the Lucasfilm document.

Lucas with Ewan McGregor, who recently said Phantom Menace was "flat"

Many devoted Star Wars fans were disappointed by The Phantom Menace, which was criticised for having a weak plot, stereotypical characters and an over-reliance on computer effects.

Lucasfilm has also conceded that the associated toys for the film were "over-licensed," "over-shipped" and "over-saturated".

The merchandising operation for the film was so vast that much stock was left unsold, disenchanting toy shops and other retailers.

Pepsi alone manufactured eight billion cans of Star Wars soft drinks for The Phantom Menace - Lucas' first directorial effort in 22 years.

Phantom Menace did great business worldwide

Lucasfilms is having no soft drink sponsor for Attack Of The Clones, and the number of licences for associated merchandise has been cut by two-thrids.

British actor Ewan McGregor, who starred as the young Obi Wan Kenobi in Episode I, has also said he thought the film was "disappointing" and "flat".

But in an interview for the FilmFour website, he said the next in the series was "much better".

"I think there's much more humour and there's much more colour - it's more reminiscent of the original three Star Wars films than Episode I was."

Attack of the Clones opens worldwide on 16 May.