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With the holiday shopping season underway, an industry group for video games is trying to encourage parents to use its voluntary ratings to protect children from graphic images of sex and violence.

The Entertainment Software Rating Board said Thursday it would distribute four public-service television spots to more than 800 broadcast and cable stations nationwide.

"Just like movies and TV shows, video games are created for a diverse audience of all ages, and some are simply not intended for children," ESRB president Patricia Vance said.

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Sens. Joe Lieberman, D-Conn., and Hillary Rodham Clinton, D-N.Y., lent their support at a Capitol Hill news conference.

Both have been active in the fight to protect children from sexually explicit and graphically violent videos, music and movies.

Lieberman said parents must play a central role in learning about the ratings and what games their children should be playing.

"Ultimately, this is about parents exercising some responsibility," Lieberman said.

Vance said about 12 percent of the games the ESRB rates each year are M-rated, intended for those aged 17 and over. She said parents should take such ratings seriously in deciding if the content of the game is appropriate for their child.

Executives from retailers Best Buy Co. (BBY) and GameStop Corp. (GME) appear in the ads, stressing their support for ratings and their store policies not to sell M-rated games to children under 17 without parental permission.

The ESRB rating system was created in 1994 by the entertainment software industry. Use of the ESRB seal and rating is voluntary, though virtually all games do so.