A spokeswoman for the prosecutor's office in the western city of Frankfurt confirmed to AFP a report in news magazine Der Spiegel that the officer had an unspecified quantity of strontium 90, a dangerous carcinogenic element, in his possession.

He will now face charges of "unauthorised handling of radioactive material" in addition to violations of the military weapons control act.

Investigators had uncovered the cache believed to belong to the army captain in a raid in the western town of Aldenhoven earlier this month.

The defence ministry said at the time that the arms were not believed to belong to the German military. Spiegel reported Friday citing ministry records that most of the stash came from former communist bloc countries.

It included Kalashnikov rifles, anti-tank and anti-aircraft weapons as well as grenades.

The suspect, who was not named, works for a military centre analysing improvised explosive devices.

Spiegel said that in addition to the strontium 90, which can be used in medicine and industry as well as be found in waste from nuclear power plants, the man also had classified documents.

The report said the papers from the BND foreign intelligence agency dealt with the situation in North Korea, and that the military anti-espionage service had joined the investigation against him.

The developments come amid a string of allegations of wrongdoing by current and former members of the German military.

Two ex-soldiers were arrested this week, accused of trying to form a "terrorist" paramilitary band of mercenaries to fight in Yemen's civil war.

In early October, the army suspended soldiers in its ceremonial guard over suspicion of sexual aggression and sympathy with the far right.

The elite KSK commando force was partially dissolved in 2020 after munitions were stolen and members were seen performing a Hitler salute at a party.

And in May, the trial opened of a German soldier who allegedly plotted to attack prominent politicians while posing as a Syrian refugee -- a bizarre case further fuelling concerns over right-wing extremism.