LOS ANGELES — Universal Music Group sued MySpace.com yesterday, alleging the social networking site that bills itself as a source of "user-generated" content instead trades on "user-stolen" songs and music videos.

The suit, filed in U.S. District Court in Los Angeles, described MySpace as a "vast virtual warehouse" of pirated works from some of label's best-known artists, including Mariah Carey, Diana Krall and U2. Universal claims "no intellectual property is safe" from the infringement, even unreleased albums such as hip-hop artist Jay-Z's upcoming "Kingdom Come."

Universal alleged MySpace is not only aware of the infringement, but it makes money selling advertising to the millions of users attracted by the lure of free access to copyrighted works.

In a written response, MySpace said it does not "induce, encourage or condone" copyright violation in any way. Indeed, yesterday it announced a new tool that makes it easier and faster for content holders to remove unauthorized content from the site.

This lawsuit pits the world's largest music label against media mogul Rupert Murdoch and his News Corp., which acquired MySpace for $580 million in September 2005.

MySpace said it is protected under the Digital Millennium Copyright Act of 1998, which provides special legal protections known as "safe harbors" to Web-hosting sites that remove copyrighted works after receiving takedown notices from the content owners.

Mark Litvack, an entertainment lawyer with Manatt Phelps & Phillips, said such court battles will ultimately determine how far Web sites like MySpace must go in policing content.

"If the music is up there without authorization, there's no dispute. It's infringement," said Litvack. "Now the question is who's responsible? There's no doubt that the poster is. The question is what MySpace's obligation is."

Michael S. Sherman, chairman of the Entertainment Group for law firm Jeffer, Mangels, Butler & Marmaro, said MySpace's safe-harbor defense may be undermined because the site sells advertising tailored to the content of the songs, music videos and artist pages.