The military's counterintelligence service (MAD) revealed on Tuesday that it has been investigating "several suspects" in a technical quality management unit in Ulm over alleged participation in the so-called "Citizens of the Reich" or "Reichsbuerger" movement.

Adherents of the movement question the legitimacy of the modern Federal Republic of Germany and have in the past entered into armed confrontations with police.

A day later, the ministry confirmed that an individual in the same unit has committed suicide, with German media including broadcasters ARD and SWR identifying him as the key suspect in the Reichsbuerger probe

A defence ministry spokesman confirmed that a "civilian worker" at the Ulm unit killed himself but would neither confirm nor deny reports that the individual was under investigation.

The latest Reichsbuerger probe follows a string of scandals in Germany in recent months over far-right networks in the police and military, with pressure mounting on the government to address the issue.

Defence Minister Annegret Kramp-Karrenbauer ordered the partial dissolution of the KSK commando force in June after revelations that some of its members harboured neo-Nazi sympathies.

The elite force is charged with sensitive and risky missions such as hostage rescue operations or anti-terror action abroad.

The MAD has also said some 600 Bundeswehr soldiers were suspected of right-wing extremism, including 20 in the elite force.