Germany is expelling four employees of the Syrian embassy.
Foreign Minister Guido Westerwelle said on Thursday that the move followed the arrest of two people on Tuesday who were suspected of spying on Syrian opposition figures in Germany.
Prosecutors believe the men had been spying for years for Syrian intelligence services.
The Syrian ambassador in Berlin was summoned to the German foreign office on Tuesday.
Deutsche Welle Radio reports the Berlin state domestic intelligence agency has been watching a number of people connected to the Syrian embassy who are considered suspicious, for several months.
There is no special programme to protect supporters of opposition groups or politically persecuted immigrants in Germany. But the constitution and the criminal code apply to every person on German soil.