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

The firm said the requests related to 18,000-19,000 user accounts and covered criminal and national security issues.

Leaks by an ex-government worker this month suggested a much larger electronic spying operation than had previously been admitted.

The US maintains the programme helped thwart dozens of terrorist attacks.