Most of the officers allegedly involved worked at some point at the same police precinct in Muelheim an der Ruhr, Reul said. All 29 were suspended with immediate effect on Wednesday, and disciplinary proceedings opened.
“We have to ask unpleasant questions of ourselves,” Reul said. “Who knew about this? Why was this tolerated for years? By whom?"
The case puts a spotlight on neo-Nazi ideology in Germany's police forces, an issue that senior security officials had previously downplayed even as they warned of the growing threat of far-right violence in recent years.
Germany’s opposition Green party called for a nationwide review of extremism in the police force.
Germany's top security official at the federal level, Horst Seehofer, had rejected calls two months ago for an investigation into the extent of racial profiling by the police, insisting that there was “no structural problem.”
On Wednesday, Seehofer's spokesman cautioned against making "sweeping allegations against the whole German police, with 300,000 officers.
“But of course it's clear, as the current case shows, that we're not talking about individuals,” said the spokesman, Steve Alter.
Similar group chats between police officers or recruits containing far-right material have been discovered in three other German states in recent years.