Russia has turned increasingly to blackmail and financial incentives to hire Germans to spy for it after the blow dealt to its intelligence services by Europe's expulsion of some 600 Russian diplomats, Germany's domestic security service said.

The Federal Office for the Protection of the Constitution (BfV) said Russian intelligence services were spending big to recruit agents in Germany despite Western attempts to limit their operations since Moscow's invasion of Ukraine.

"Russia is working hard to compensate for the German government's reduction in the number of Russian agents in Germany," BfV chief Thomas Haldenwang told a news conference.