German Interior Minister Horst Seehofer on Tuesday said authorities are working under the assumption that the murder of a politician in the central German city of Kassel was politically motivated.

"According to what we know, we must now assume that the perpetrator is a right-wing extremist and that the crime has a right-wing extremist backdrop," Seehofer said at a press conference.

Walter Lübcke, district president of Kassel and supporter of Chancellor Angela Merkel's open door policy for refugees, was shot dead earlier this month. He received a bullet wound to the head in what appeared to be an execution-style assassination.

Read more: Walter Lübcke murder raises specter of neo-Nazi terrorism

'Alarm bell'

The main suspect, identified by German media as Stephan E., is believed to be a far-right sympathizer. Federal prosecutors took over the case on Monday, one of the first signs the murder was the result of a politically motivated attack. Seehofer confirmed those suspicions on Tuesday.

"A right-wing extremist attack on a leading representative of the state is an alarm bell and is directed against us all," Seehofer said. "Right-wing extremism is a considerable and serious problem to our free society."

If prosecutors prove that the murder was politically motivated, it would be the first of its kind on a sitting politician in Germany since the 1970s. Federal prosecutors on Monday said there was no evidence to suggest the suspect was part of a far-right network.

Read more: Extremist crimes in Germany down, number of fanatics up

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ls/ng (dpa, AFP)