German authorities arrested two men on suspicion of a possible attack plot in the West German city of Duisburg on Friday morning.

The Kosovo-born brothers, aged 28 and 31, are suspected to plan an attack on the Centro mall, one of Germany’s largest with 250 shops and an adjoining seasonal Christmas market, located about ten miles from Duisburg in Oberhausen.

The detention came after a large-scale police operation at the shopping center on Thursday night upon a threat alert sent by the Office for the Protection of the Constitution. At present, a link to the Berlin incident is not apparent, and investigators are trying to shed light on the stage of preparation, possible accomplices and motives.

Security forces were already stepped up nationwide after a lorry hit the Christmas market at Berlin’s Breitscheidplatz, killing 12 people and wounding dozens more, in an alleged Islamic assault by suspect Anis Amri.

At the time of the operation in Oberhausen and the arrest in Duisburg, Amri, who was shot on Friday, was still assumed on the run.

Meanwhile, the Christmas markets in Berlin as well as the Centro mall remain open, albeit slightly less frequented. “We are continuing business as usual”, the management offices of the shopping center told WWD on Friday.