For the first time, Google, Facebook and other leading Internet companies issued reports Monday about previously secret U.S. government demands for their users' data, while renewing their call for reform of surveillance programs that have become a major source of friction between Silicon Valley and Washington, D.C.

The companies said the government's demands under the Foreign Intelligence Surveillance Act involved 59,000 or more Internet accounts in the first half of last year. Company officials said those numbers represent a small fraction of their hundreds of millions of users, and include many cases in which a single individual holds multiple accounts.

Stung by a series of news reports about government surveillance, based on documents leaked by former National Security Agency contractor Edward Snowden, the companies have been eager to show they hand over users' data only under narrow circumstances. The new reports were allowed under a legal settlement reached after several companies sued the government to loosen the rules that prevented them from disclosing such demands in the past.

Companies were previously allowed to report on certain types of requests, including those known as National Security Letters, but not demands issued under the FISA law. Even so, the recent settlement still requires the companies to describe the requests in broad categories and report the numbers in ranges of 1,000.

In addition, the reports don't reflect the whole picture of government surveillance, as Microsoft General Counsel Brad Smith acknowledged in a blog post Monday.

"Nothing in today's report minimizes the significance of efforts by governments to obtain customer data outside legal process," Smith wrote. Citing news reports about U.S. efforts to hack into the data cables between some companies' computer centers, Smith added, "this has been and remains a major concern across the tech sector."