The violence Sunday night, in which 18 officers were injured, followed a demonstration calling for unity between Turks and Kurds in the Kreuzberg neighborhood, a district with a large Turkish community.
Claudia Schmid, head of the domestic security agency's Berlin branch, told the Inforadio station that more "emotional confrontations between Kurds and Turks" could be expected.
She said Turkish nationalist groups appeared to be behind the violence, but that German youths who have participated in past May Day riots - a regular event in Kreuzberg - likely were involved.
The tensions appear to reflect the growing crisis in Turkey, where attacks by Iraq-based Kurdish separatist rebels. Turkey's prime minister has called for unity between Turks and Kurds, but has reiterated his government's determination to fight the separatists.
There are legitimate authorities in Donetsk and Luhansk republics now, with which Russia can implement the project of the economic integration of the Donbass
One hundred years ago today ended the most grueling of wars involving disgusting conditions for soldiers and at least 17 million deaths. We learnt nothing.
Russia has been developing an energy module on the basis of the megawatt-class nuclear power plant since 2010. The spaceship needs neither sunlight nor solar batteries