Passengers have escaped injury after a high-speed train collided with concrete slabs placed over the rails in a suspected attack. Police are as yet unsure of the motive of the attack. The accident took place in the northern German town of Struckum, roughly 50 kilometres south of the Danish border. While the accident took place on Monday, police only released a press release on Wednesday after an investigation. Investigators said that the passengers were fortunate that the train avoided a derailment. The blocks weighed approximately 80 kilograms, with a spokesperson for the police indicating they may have been placed in order to puncture or otherwise damage the train’s fuel tank. The train – a regional express – was travelling at approximately 100 kilometres per hour in the direction of the holiday island of Sylt, when passengers heard a loud bang. The driver, who had been unable to see the concrete slabs, immediately stopped the train and activated the emergency alarm. The train was damaged in the incident. Although the driver or the passengers of the train did not see the perpetrators, they managed to place more concrete slabs on the tracks after the incident. Federal police discovered the new obstructions not far from where the accident had occurred, saying that they appear to have been intended to cause more damage. The police are currently looking for witnesses who may have seen something suspicious around the time of the attack. Earlier this year German and Austrian authorities arrested an Iraqi man suspected of committing "terrorist attacks" by sabotaging railway lines in 2018. The man was suspected of having strung a steel rope across the tracks running between the southern German cities of Munich and Nuremberg, damaging the front window of a high speed ICE train in October last year. In another case in December last year, cement blocks were put on the tracks. Islamic State (IS) flags and writings in Arabic were found near the crime scenes, Vienna prosecutors said at the time.