Facebook received 9,000-10,000 requests for user data from US government entities in the second half of 2012.

◼ NSA snooping: Facebook reveals details of data requests - BBC

The social-networking site said the requests, relating to between 18,000 and 19,000 accounts, covered issues from local crime to national security.

Microsoft meanwhile said it received 6,000 and 7,000 requests for data from between 31,000 and 32,000 accounts.

Leaks by a former computer technician suggest the US electronic surveillance programme is far larger than was known.

Internet companies - including Facebook, Google, Yahoo, Apple and Microsoft - were reported last week to have granted the National Security Agency (NSA) "direct access" to their servers under a data collection programme called Prism.

The firms denied the accusations, saying they gave no such access but did comply with lawful requests....

In an effort to reassure its users, Facebook lawyer Ted Ullyot wrote on the company's blog that following discussions with the relevant authorities it could for the first time report all US national security-related requests for data.

"As of today, the government will only authorise us to communicate about these numbers in aggregate, and as a range," he said.