German Transport Minister Volker Wissing said Saturday that "sabotage acts on the cable network" were responsible for a serious outage of train traffic in large parts of northern Germany, adding that authorities were investigating and seeking the unknown perpetrators.

The service of long-distance, regional and cargo trains in the northwestern states of Hamburg, Schleswig-Holstein, Lower Saxony and Bremen was interrupted for about three hours on Saturday morning after critical cables for a communication system, which enables radio contact and data transmission between trains and the railway operating centers, had been sabotaged.

"We know that cables have been cut at two sites," Wissing said, speaking of "deliberate and malicious" acts. Wissing did not provide further information on who could be behind the attack, saying that authorities were investigating the case.

German media reported that the extent of the sabotage required an extensive knowledge of the communication infrastructure of German railway operator Deutsche Bahn.

Deutsche Bahn said at 11 a.m. on Saturday that the disruption of communication services had been resolved and that rail traffic was starting again.