An act of "sabotage" targeting communications infrastructure was to blame for major disruption on the German railway network on Saturday, operator Deutsche Bahn said.

"Cable sabotage" was the cause of the breakdown, which led to a three-hour suspension of train services throughout northern Germany, a spokesman for the company said.

There was damage to the GSM-R, a radio network used for communication on the railway, Der Spiegel reported, quoting security sources.

The cables could have been cut "in two places," it added.

Any action against the cable would require "certain knowledge" of the rail system, the Bild daily said, adding that federal police were investigating.

Traffic was completely interrupted for about three hours because of "a breakdown in the digital radio system for the trains", before being restored, according to Deutsche Bahn.

Services were affected between Berlin and regions in the west and north of the country including Schleswig-Holstein, the cities of Hamburg and Bremen, as well as Lower Saxony and parts of North Rhine-Westphalia.

The Berlin-Amsterdam route was also suspended.

Cancellations and delays were still expected on Saturday despite the restoration of rail services, Deutsche Bahn warned.

The attack comes just over two weeks after sabotage attacks on the Nord Stream 1 and 2 gas pipelines linking Russia and Germany.

The German government has also stepped up protection of its critical infrastructure. (AFP)