Microsoft said on Tuesday it has written to the U.S. Attorney General to ask for more freedom to disclose how it handles requests for customer data from national security organizations. The letter comes a week after the Guardian newspaper reported that Microsoft allowed U.S. security agencies to circumvent encryption of Outlook emails and capture Skype online chats.

Microsoft has said there were "significant inaccuracies" in the media reports last week and asserted it does not allow any government direct or unfettered access to customers' emails, instant messages or data.

"We believe the U.S. Constitution guarantees our freedom to share more information with the public, yet the Government is stopping us," Microsoft 's lawyer Brad Smith said in a blog on Microsoft's website.

He said government lawyers have not responded to a court motion made in mid-June asking for permission to publish the volume of requests it has received.

So far, the U.S. government has restricted what companies can say under about the requests under the highly secret Foreign Intelligence Surveillance Act.