Twenty-nine police officers in the western German state of North-Rhine Westphalia have been temporarily suspended after their unit was found to have shared extreme rightwing content on a WhatsApp group.

Images shared by the officers, most of whom are members of a unit in the town of Mülheim an der Ruhr, reportedly depicted Adolf Hitler, the swastika flag, a collage of a refugee inside a gas chamber and the shooting of a young black person.

The swastika is on the German criminal code’s list of “symbols of unconstitutional organisations” and sharing the symbol via chat groups can be punished under German law.

The 126 files were shared via five different chat groups, with most images sent in 2015, at the height of the European refugee crisis in Germany. The most recent message under investigation was sent on 27 August this year.

At a press conference on Wednesday, the interior minister of North-Rhine Westphalia, Herbert Reul, described the findings as a “disgrace” for police forces in his state, which had “shaken police to the bone”.

“Rightwing extremists and neo-Nazis have no place in the North Rhine-Westphalian police force, in our police force,” Reul said.

On Wednesday morning authorities searched 34 apartments and offices with links to the officers under investigation, in the towns of Duisburg, Essen, Mülheim an der Ruhr, Oberhausen, Moers and Selm.

The officers under investigation include six women. Eleven officers who are believed to have actively sent the images are under investigation for incitement of the people and the use of symbols of unconstitutional organisations. The remaining 18 officers are understood to have merely received the messages without reporting it to higher authorities.

The chat group’s existence and content had emerged by chance, after authorities in Mülheim had confiscated the mobile phone of a police officer who was being investigated for sharing classified information with a journalist.

Reul said on Wednesday he expected further disclosures as the confiscated phones were examined.

The scandal comes just two months after the federal interior minister, Horst Seehofer, halted a planned study into allegations of racial profiling by German police forces.

The study, which was in the “conceptual development” stage, was reportedly cancelled with the reasoning that racial profiling by federal police did not have to be separately examined because it was already prohibited.