Google Inc accused Viacom Inc of secretly uploading its videos to YouTube even as the media conglomerate publicly denounced the online video site for copyright infringement, according to court documents made public on Thursday.

Google also claimed Viacom had in 2006 expressed interest in buying YouTube, which the Web search leader subsequently bought in October that year for $1.65 billion.

YouTube was sued by Viacom for $1 billion for alleged copyright infringement in March 2007, in the U.S. District Court in Southern New York.

The opening briefs in the Viacom vs YouTube lawsuit are widely seen as a test of the Digital Millennium Copyright Act (DMCA) which YouTube believes protects it from Viacom's claims.

Viacom owns cable networks like MTV, BET and Nickelodeon.

While it is still early in the legal battle it was clear that Google was determined to cast Viacom's legal strategy as hypocritical by claiming several of the company's own managers and agencies had continued to upload videos to YouTube.

Viacom routinely left up clips from shows that had been uploaded to YouTube by ordinary users, said YouTube Chief Counsel Zahavah Levine, in a blog post.

Executives as high up as the president of Comedy Central and the head of MTV Networks felt very strongly that clips from shows like The Daily Show and The Colbert Report should remain on YouTube, Levine said in the post.

But Viacom also accused Google and YouTube executives of hypocrisy, saying that they were aware of the extent of illegally uploaded videos to the site and did little to stop it as they sought to build their user base.

Google and YouTube were not just innocent and unwitting accomplices to infringement perpetrated by YouTube users, Viacom said in the court documents. Defendants operated YouTube with the unlawful objective of using infringing material to explosively build their user base and become the dominant video website on the Internet.

The case is In re: Viacom v. YouTube, U.S. District Court for the Southern District of New York, No. 1:07-cv-02103 (LLS).

(Reporting by Yinka Adegoke and Alexei Oreskovic in San Francisco; Editing by Richard Chang)