Facebook's local servers in Vietnam were taken offline early this year, slowing local traffic to a crawl until it agreed to significantly increase the censorship of "anti-state" posts for local users, two sources at the company said Tuesday.

The restrictions, which the sources said were carried out by state-owned telecommunications companies, knocked the servers offline for around seven weeks, meaning the website became unusable at times.

"We believe the action was taken to place significant pressure on us to increase our compliance with legal takedown orders when it comes to content that our users in Vietnam see," the first of the two Facebook sources said.