A Syrian refugee whose selfie with German chancellor Angela Merkel went viral is suing Facebook for defamation, his lawyer said, after the social networking site failed to take down a series of posts accusing him of being a "terrorist" and criminal.

Anas Modamani, a 19-year-old refugee from Damascus, was pictured in September 2015 taking a selfie with Merkel during her visit to a refugee shelter in Berlin's Spandau district.

The image came to define Germany's response to the refugee crisis, when Merkel opened the country's borders to hundreds of thousands of asylum seekers.

But, in the following months, Modamani's image was shared on Facebook on a series of anonymous accounts, alongside posts claiming he was responsible for attacks and murder, including the Brussels Airport bombing of March 2016.

Facebook has repeatedly refused to take the posts down, saying they do not violate the company's rules, Modamani's lawyer said.

"Whenever something happens in the news related to refugees, his picture reappears," Modamani's lawyer, Chan-jo Jun, told the Thomson Reuters Foundation.

A Facebook spokesperson told Britain's Guardian newspaper they had received a takedown request from Jun "alleging that a specific item of content on our platform violates Mr Modamani's right of personality.

"Access to that reported content was quickly disabled, so we do not believe there is any basis for him to seek an injunction," the spokesperson said.

Angela Merkel Takes Selfie With Brussels Terrorist. Still wonder why Germany is flooded with rapefugees? #BanIslam pic.twitter.com/fYRPkOuAEK — Stop Islamization (@rally_texas) May 10, 2016

One post falsely linked Modamani to an incident in Berlin last month, when a group set fire to a sleeping homeless man on a train station platform, Jun said.

The post was shared 500 times and was likely to have been seen by at least 25,000 people, he said.

Jun filed a preliminary injunction against Facebook Europe in December, and a court hearing is scheduled for February 6 in Wurzburg, southern Germany, he said.

The case comes as Germany's justice ministry considers new policies to crack down on "fake news" by making Facebook and other social media companies criminally liable for failing to remove hate speech.

Facebook should be treated as a media company rather than a technology company, the justice minister said in November.

Modamani now works in a fast-food restaurant in Berlin, his lawyer said.

Mark Zuckerberg, Facebook's chief executive, announced a series of measures in November to stem a flood of "fake news" articles in the wake of the US presidential election.

He said Facebook would make it easier for users to report fake news, and more difficult for fake news providers to make money through its advertising system.