Story highlights Police searched an apartment, questioned its owner in connection with the threat

Germany remains on edge after a pair of deadly incidents last year

(CNN) German police shut down a large shopping mall in the western city of Essen on Saturday following "concrete indications" of a possible terror attack, a police spokesman said.

Hundreds of police are involved in the security operation at the Limbecker Platz mall, which was locked down before it opened to the public, Essen police spokesperson Christoph Wickhorst said. Police officers and vans surrounded the mall -- one of the biggest in Germany -- Saturday afternoon, Reuters reported.

Details of the threat weren't immediately available. But the closure comes a day after police received very serious indications from "another agency" that an attack was possibly planned on the mall Saturday, Wickhorst said.

Police were also searching an apartment in the city of Oberhausen, about 12 miles from Essen, and questioning the apartment's owner, according to a police statement. The apartment search is directly related to the mall threat, police spokesperson Peter Elke told German broadcaster NTV.

A second man who was picked up at an Internet cafe was also being questioned, said police, who intend to search his apartment.

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