The number of investigations into suspected terrorist activities has soared in Germany this year, to around five times as many as 2016, the federal prosecutors office says.

Around 1,200 investigations were opened in 2017, a spokesman for the federal prosecutors office in the city of Karlsruhe told German Press Agency.

In 2016 by comparison there were around 250 cases.

The high caseload has forced federal prosecutors to hand around a third of terrorism cases to their state colleagues.

Sven Rebehn, chairman of the German Association of Judges, says the number of cases passed on has been significantly higher in 2017 than in previous years, with state prosecutors in Dusseldorf, Berlin, Frankfurt and Hamburg most affected.