Police guard a shopping mall Saturday in Essen, Germany, amid a terror threat.

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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.

The mall will “remain closed this Saturday for security reasons,” a message on the shopping center’s website said.

“Police have concrete indications of a possible attack. In order not avoid any danger for visitors the closure has been ordered,” the mall’s website message said.

Essen, in the western province of North Rhine-Westphalia, is a city of about 590,000 people.

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

Two passers-by stand Saturday outside the Limbecker Mall in Essen, Germany. The mall was closed due to a terror threat.

Twelve people were killed and 48 others injured in December after a tractor-trailer plowed through a busy outdoor Christmas market in Berlin. The suspect, a Tunisian man, was shot dead by police days after the attack, which ISIS claimed it inspired.

In July, nine people were killed and 16 people injured in a shooting rampage at a busy shopping district in Munich. Police said the attacker was a mentally troubled 18-year-old who had extensively researched rampage killings. The man, who had no apparent links to ISIS, fatally shot himself shortly after the attack, police said.

CNN’s Michelle Krupa contributed to this report.