The assailants threw the incendiary devices against the façade of the facility, located in the Ruhr valley city of Dortmund. One device broke through a window when it was thrown but did not ignite. The others went out after they were thrown and failed to cause appreciable damage.
No one was in the building at the time of the attack.
One resident in the neighbourhood reported that a loud bang attracted his attention at around 4 am Sunday morning. He said he saw three or four youths at the scene, but could not provide a description of them.
Police so far have no other information about the background of the attacks and have begun an investigation.