Amid escalating combat, Iraq has blocked Facebook, Twitter and other social media.
Users in the country attempting to view these sites are met with a message saying the Ministry of Communications has barred access.
The move comes after Islamist insurgents used Twitter to post a graphic image of a beheaded man.
A system which allows users to circumvent internet censorship, known as Psiphon, said they had seen a huge influx in the number of those using its service.
On Sunday, more than 500,000 people used Psiphon, up from around 8,000 on an average day.
Anti-censorship organisations have reacted negatively to the block, saying it harmed those using the site for legitimate purposes.
Jillian York, director for international freedom of expression at the Electronic Frontier Foundation, which campaigns for civil liberties said: "The Iraqi government will not achieve anything by blocking social media websites, rather, in doing so, they're cutting off a lifeline for activists and others to the outside world."
A Facebook spokesperson added: "We are disturbed by reports of access issues in Iraq and are investigating. Limiting access to internet services - essential for communication and commerce for millions of people - is a matter of concern for the global community."
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