On Monday, a device knocked out signals on the busy rail route from Berlin to Hamburg, causing hours of delays as high-speed trains had to be diverted.
An extreme leftist group later claimed responsibility in emails to news agencies and on an online forum used by extremists. It wrote it was protesting German involvement in Afghanistan and called for US soldier Bradley Manning, charged with leaking classified documents to Wikileaks, to be released.
The so-called “Hekla reception committee” warned of more attacks, saying it wished to see life in Berlin disrupted.
That same day, police also said they foiled an attempted attack in a tunnel near Berlin's main train station after staff stumbled upon suspicious objects described as incendiary agents similar to those used in the arson attack. Police officers defused the devices.
In Tuesday's incident, a Deutsche Bahn worker found two bottles containing flammable liquid on train tracks in southeastern Berlin. The federal police closed off the area for investigation.
It is not yet clear if the bottles simply had not been found Monday or if they were placed there after the first incidents.
Since Monday more than 300 trains have been delayed due to the arson attacks, with a few cancelled altogether, mostly on the Berlin to Hamburg line. A Deutsche Bahn spokesperson said officials were trying to get everything back on schedule by Wednesday.
Transportation problems promised to deepen Tuesday, as Berlin authorities shut down multiple S-Bahn lines as a precaution. They promised to work on alternative travel arrangements for stranded passengers.
This isn't the only time Berlin's rail network has been targeted by leftist extremists. An attack on a switching box in May disrupted train service for a large swathe of the capital.