Three of the largest Internet companies called on the US government to provide greater transparency on national security requests.

The companies are seeking to distance themselves from reports that portrayed the companies as willing partners in supplying mass data to security agencies.

In similarly worded statements released within hours: Google Inc, Microsoft Corp and Facebook Inc all asked the US government for permission to make public the number and scope of data requests each receives from security agencies.

Each of the companies, and several others, have come under scrutiny following reports.

The disclosures were revealed in The Guardian and Washington Post newspapers of their role in a National Security Agency data collection programme named Prism.

Google was the first to go public, releasing an open letter asking the US Department of Justice for permission to publish the total number of government requests for national security information.

It argues the figures would show the company does not give the government "unfettered access" to its users' data.

Google Chief Legal Officer David Drummond said: "Assertions in the press that our compliance with these requests gives the US government unfettered access to our users' data are simply untrue."

Google's current transparency reports, which show the number of data requests it receives from authorities, do not include requests under the Foreign Intelligence Surveillance Act (FISA).

Microsoft issued a similar request saying: "Permitting greater transparency on the aggregate volume and scope of national security requests, including FISA orders, would help the community understand and debate these important issues," Microsoft said in an emailed statement.

Leading social network Facebook followed within minutes.

Facebook's general counsel Ted Ullyot said: "We would welcome the opportunity to provide a transparency report that allows us to share with those who use Facebook around the world a complete picture of the government requests we receive, and how we respond,"

Mr Ullyot said: "We urge the United States government to help make that possible by allowing companies to include information about the size and scope of national security requests we receive, and look forward to publishing a report that includes that information."

President Barack Obama and senior US intelligence officials have confirmed the existence of Prism.

Google and other tech firms have vigorously denied that they give government agencies direct access to their servers.

They also deny that they comply with overly broad requests for user data.