More than a dozen vandals threw rocks, smoke bombs and paint at the Facebook headquarters in the northern city of Hamburg in Germany, smashing windows and spray-painting the phrase "Facebook Dislike" on a wall of the building, police in the area said on Sunday.

According to reports, a group of 15 to 20 masked individuals clad in black clothes and hoods carried out the attack overnight around 20:00 GMT Saturday. An investigation has begun to find the perpetrators, who fled on foot.

A Facebook spokesperson said that no one was injured. The company was not available for an immediate comment regarding the matter. The motive for the incident is yet to be determined.

Facebook allegedly failed to filter hate-filled racist content on the social network, where the European head of the company is under an ongoing investigation.

The case was announced last month when German celebrities and politicians openly spoke of the anti-foreigner comments on Facebook and other social media platforms as Germany copes with the rapidly increasing number of refugees in the country.

A spokesperson for the prosecution said at the beginning of the investigation that the failure to remove the racist comments could be attributed to Martin Ott, managing director for northern, central and eastern Europe of Facebook.

"[W]e can say that the allegations lack merit and there has been no violation of German law by Facebook or its employees," a Facebook representative says, declining to comment regarding the investigation.

German critics say that Facebook focuses more on filtering sexual content and nudity rather than hate speech.

"[Facebook must not] become a funfair for the far-right," Heiko Maas, federal minister of justice and consumer protection, says.

In light of the development, Facebook says that it will encourage "counter speech" in an effort to cut down xenophobic behavior on the social network. With that said, the company holds a partnership with FSM, a group that voluntarily monitors multimedia service providers.

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