German police officers arrested two brothers on suspicion of planning to attack one of the country's biggest shopping centres in the western city of Oberhausen.
The men, aged 28 and 31, are originally from Kosovo, and were arrested late yesterday.
Investigators were trying to establish what stage of preparation the plot was at and whether others were involved, police said.
The brothers are alleged to have been targeting the Centro shopping centre, which has more than 250 stores.
Separately, police in Germany carried out raids across Germany as a Europe-wide manhunt continues for Anis Amri - the main suspect in the Christmas market attack which has been claimed by Islamic State.
The failed asylum seeker is suspected of being behind the wheel of the truck during the attack that killed 12 people and injured 56.