Facebook received 9000-10,000 requests for user data from US government entities in the second half of 2012.

The social networking site said the requests, relating to 18,000-19,000 accounts, covered issues including national security. Microsoft said it received 6000-7000 requests for data.

US attorney general Eric Holder is vowing to bring to justice Edward Snowden, accusing the former intelligence contractor who leaked surveillance information of endangering the safety of Americans and their allies.