Berlin police are investigating an assault on a city journalist who was attacked after writing a column critical of anti-immigrant movements in the country.

The Tagesspiegel newspaper said Monday that their journalist, whose name was not given, was hit from behind on Friday by someone who identified him and the newspaper by name, and called him a "filthy leftist pig," the dpa news agency reported.

The paper called it not only an attack on a colleague but "on the freedom of the press and freedom of opinion."

The journalist, who was not seriously hurt, had on Thursday penned a column critical of the anti-Islamic PEGIDA movement, the populist AfD party and more general anti-immigration sentiment.

Berlin's top security official, Frank Henkel, says "violence, intimidation and hate" will not be tolerated.