Google has said it will defend itself against allegations that YouTube, the video-sharing website it owns, is enabling widespread copyright infringement.

In March, Viacom, the entertainment company which owns MTV and Nickelodeon, filed a $1 billion (£500 million) claim against the search company accusing it of allowing more than 160,000 clips of its programming to be illegally uploaded.

Yesterday Google denied that YouTube was infringing copyright, saying that it removed authorised videos from the site when asked by content owners, as required by United States law, and accused Viacom of "threatening the way millions of people legitimately exchange information, news, entertainment and political and artistic expression".

"Google and YouTube respect the importance of intellectual property rights, and not only comply with their safe harbor obligations, but go well above and beyond what the law requires," the company said in a submission filed with a court in San Francisco.

In the filing, Google admitted that some "third parties" had "enabled users" to make "unauthorised use of the YouTube service", but its lawyer said that when Viacom had asked YouTube to take down more than 100,000 videos recently, it had complied with the request.

Google's defence relies on so-called "safe harbours" in the Digital Millennium Copyright Act (DMCA) of 1998 which protect content-hosting sites such as YouTube and Craigslist so long as they take down copyright-infringing material if the copyright owner requests.

The filing states that YouTube provides copyright owners with tools that enable them to find clips that have been illegally uploaded and these tools "can prevent the reloading of copies of the same video clip after it has been removed from the service".

In response to Google's filing, Viacom said: ''This ignores the most important fact of the suit, which is that YouTube does not qualify for safe harbor protection under the DMCA. It is obvious that YouTube has knowledge of infringing material on their site, and they are profiting from it."

The two companies have been engaged in a war of words since negotations to reach an agreement about the use of content broke down in February.

In its initial lawsuit, Viacom said: "Some entities, rather than taking the rightful path of building businesses that respect intellectual property rights on the internet, have sought their fortunes by brazenly exploiting the infringing potential of digital technology. YouTube is one such entity."

This week Michael Kwun, the managing counsel for litigation at Google accused Viacom of "attempting to rewrite copyright law through a baseless lawsuit" and told reporters: "We are not going to let this lawsuit distract us. We feel pretty confident about the case and are ready to take it to court."

An initial hearing, at which the judge may set a timeline for the trial, is scheduled for July.

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