A Japanese entertainment group has asked the popular video-sharing site YouTube Inc. to implement a system to prevent users from uploading videos that would infringe copyrights, a group spokesman said Tuesday.

The Japan Society for Rights of Authors, Composers and Publishers sent a letter making the request addressed to YouTube co-founders Chad Hurley and Steve Chen by express mail and e-mail on behalf of 23 Japanese TV stations and entertainment companies, according to Takashi Fujii, a spokesman for the Jasrac group.

Most videos posted on YouTube are homemade, but the site also features copyrighted material posted by individual users.

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YouTube's policy has been to remove clips that infringe copyright after it receives complaints, but questions have continued to linger about the site's vulnerability to legal claims for distributing content owned by other media.

Last month, YouTube — recently acquired by Google Inc. (GOOG) for $1.65 billion — deleted nearly 30,000 files after the Japanese group complained of copyright infringement.

But Jasrac said in a letter dated Monday seen by The Associated Press that the problem has persisted, and that the current system "is not functioning well due to the [continued] large volume of illegal uploads."

The letter requested that YouTube introduce a preliminary screening system to prevent copyrighted clips from being posted.

It also asked for a series of provisional measures, including posting a notice in Japanese about illegal uploads, requiring uploaders to register and terminating users who violate copyright.

The letter asked YouTube to respond no later than Dec. 15.

YouTube has been negotiating with leading copyright holders and reached agreement with several letting the Web site post copyright music videos and other content in exchange for sharing ad revenue.

The company agreed to deploy an audio-signature technology that can spot a low-quality copy of a licensed clip. YouTube would have to substitute an approved version or remove the material automatically.

YouTube has licensing deals with CBS Corp. (CBS) and three major recording companies: Warner Music Group Corp. (WMG), Vivendi SA's Universal Music Group and Sony BMG Music Entertainment, which is a joint venture between Sony Corp. (SNE) and Bertelsmann AG.

Since YouTube started in February 2005, the company has blossomed, now showing more than 100 million video clips per day.

YouTube's worldwide audience was 72.1 million by August, up 2.8 million from a year earlier, according to comScore Media Metrix.