The US government is asking a judge to force Google to hand over data on searches performed by its users, arguing that it needs the information to determine how often users search for pornography. 

A request has been filed under an internet child protection law that seeks to prevent minors from accessing websites containing adult material.

The US Supreme Court invalidated the law two years ago because it violates free speech rights and could prevent legal access to porn sites.

The government is now seeking to overturn that ruling, claiming that it needs the Google user data to build its case.

Google declined to hand over the information last year because it considered the request to be "overreaching". The refusal sparked this week's lawsuit.

A report in the San José Mercury News stated that the government had asked for one million random web addresses as well as all search queries for a one-week period. 

Other unnamed search engines have complied with the government's request.