The United States confirmed on Thursday that it was seeking the extradition of the alleged boss of the world's biggest online piracy site, Kickass Torrents, on charges of distributing over $1 billion worth of illegally copied films, music and other content.

A day earlier, the US Justice Department unveiled a criminal complaint against Ukrainian national Artem Vaulin, 30, who was arrested in Poland and is wanted by American authorities for copyright infringement, money laundering and other charges.

Vaulin is alleged to own Kickass Torrents or KAT, which in recent years has eclipsed Pirate Bay and others to become the world's biggest source of pirated media. Stephen Dreikorn, a spokesman for the US embassy in Warsaw, told AFP via email: 'We can confirm the United States government is seeking extradition of Artem Vaulin.'

The US criminal complaint said the website offers 'a sophisticated and user-friendly environment in which its users are able to search for and locate content' which is protected by copyright.

KAT -- which distributes pirated films, video games, television programmes and music -- is estimated to be the 69th most frequently visited website on the internet, according to a Justice Department statement.