Germany's state-owned railway operator blamed "sabotage" to its cables for an hours-long stoppage of all rail traffic in the north of the country on October 8, and launched an investigation into who was behind the interference.
Deutsche Bahn (DB) didn't say who it suspected and said service had since restarted.
But the outage follows a warning from the NATO military alliance and the European Union of the urgency of protecting critical infrastructure after sabotage was blamed for at least four sudden and sizable leaks last month in the Nord Stream gas pipelines that run from Russia to Western Europe.
Russia has responded to suspicions it was behind those gas leaks by calling such sabotage "unthinkable."
"Due to sabotage on cables that are indispensable for rail traffic, Deutsche Bahn had to stop rail traffic in the north this morning for nearly three hours," the German railway operator announced on October 8.
Earlier, it cited a technical problem with radio communications.
Der Spiegel magazine quoted anonymous security sources as saying cables for DB's communications network had been sliced in two places.
Rail service was affected through Lower Saxony and Schleswig-Holstein in addition to Bremen and Hamburg, and international rail journeys to Denmark and the Netherlands were also delayed as a result.
DB said no long-distance trains were running between Berlin, in the east of the country, and Hanover and North Rhine Westphalia in the west.
DB tweeted later that while many trains were running, "There are still impairments. Unfortunately, you still have to expect train and stop cancellations and delays."
The Swedish Security Police on October 6 said its initial probe confirmed that "detonations" caused "extensive damage" to the Nord Stream 1 and Nord Stream 2 pipelines last week.
Russia supplies around one-third of Europe's natural gas, which has been at the center of sanctions-related trade disputes since Russia launched its unprovoked invasion of Ukraine in February.
Before the alleged sabotage to the Nord Stream pipelines, Russia's gas provider several times cited technical holdups that it said prevented its deliveries to the West.