WASHINGTON (AFP) - Microsoft has said it received between 6,000 and 7,000 criminal and national security requests from US authorities in the second half of last year related to 31,000 to 32,000 customer accounts.

The company announced the figures late on Friday, as it and other Internet giants responded to demands for greater transparency after revelations of a vast US spying program that authorities say targeted only foreign terror suspects.

Microsoft said the requests include criminal warrants, subpoenas and orders, and that it is prohibited by law from publishing a separate tally of requests related to national security.

"This afternoon, the FBI and DOJ have given us permission to publish some additional data, and we are publishing it straight away," Microsoft's Deputy General Counsel John Frank said in a statement on Friday.

"However, we continue to believe that what we are permitted to publish continues to fall short of what is needed to help the community understand and debate these issues."

The company insisted the orders affect only a "tiny fraction of Microsoft's global customer base".

Facebook on Friday said it received between 9,000 and 10,000 requests for user data from US authorities in the second half of last year, covering issues ranging from missing children and petty crimes to terror threats.

The Facebook requests targeted between 18,000 and 19,000 accounts, the social networking site said, without revealing how often it complied with the requests.

Facebook "aggressively" protects its users' data, the company's general counsel Ted Ullyot said in a statement.

"We frequently reject such requests outright, or require the government to substantially scale down its requests, or simply give the government much less data than it has requested. And we respond only as required by law," he added.

Major Internet firms have come under intense scrutiny after government contractor Edward Snowden leaked details of a vast programme in which nine companies turned over user data to the National Security Agency.

The companies, which also include Google, Apple and Yahoo, have denied claims that the NSA could directly access their servers. US authorities have said the programme was legal and limited, and helped prevent terror attacks.

Google asked the FBI and US Justice Department this week for permission to release separate tallies related to its handing over of data for the leaked surveillance programs, saying it has "nothing to hide."