According to a court decision in Castrop-Rauxel in North Rhine-Westphalia, law enforcement officers searched the house of a 32-year-old accused Iranian citizen.
The man was suspected of preparing "an act of violence that poses a threat to the state."
According to preliminary data, he acquired cyanide and ricin for the attack.
The Iranian and another person were taken into custody, and evidence was seized for analysis.
The decision on the arrest will be made later.
According to the laws of Germany, for the preparation of such crimes, attackers face imprisonment for a period of six months to 10 years.
Earlier it was reported that the recruited agent of the SBU planned to poison one of the high-ranking officials in the Luhansk People's Republic.
The performer had to get a job as a waiter and pour the poison from the ampoule into the order.