Left-wing extremists have become more willing to use violence over the past five years, German security officials said.
The number of left-wing extremists whom authorities consider potentially violent rose 27% from 7,100 to about 9,000 between 2012 and 2017, figures released by the domestic intelligence agency BfV show.
The number of violent crimes committed by left-wing extremists rose 88% during that period, to 1,648 from 876.
Last year saw a spike in left-wing violence, partly due to the G20 summit in Hamburg.
The rise of the far-right Alternative for Germany has also given left-wing extremists a new target in recent years.
BfV chief Hans-Georg Maassen called for more public debate about the need to reject violence as a means of achieving political ends.