BERLIN (AP) — Two Kosovo-born brothers were detained Friday on suspicion that they were planning to carry out an attack on a shopping mall in western Germany, days after a truck attack in Berlin that killed 12 people.

The men, aged 28 and 31, were detained in Duisburg in the industrial Ruhr region shortly after midnight, police said.

Authorities suspect the two men may have been planning an attack on the Centro mall in nearby Oberhausen. They are investigating what the pair intended to do and whether anyone else was involved. Police said a judge allowed them to keep the men in custody until Saturday while investigators establish whether they have a solid case.

Police said in a statement that they increased their presence at Centro and a nearby Christmas market on Thursday evening after receiving a tip from “security sources.” The mall was open for business as usual Friday.

Centro is one of Germany’s biggest malls, with more than 250 shops. It opened 20 years ago on the site of a former steelworks.

Interior Minister Thomas de Maiziere said there was “no connection” between the Oberhausen case and the Berlin attack.

The chief suspect in the Berlin case, 24-year-old Tunisian Anis Amri, was killed in a shootout with police in the Italian city of Milan early Friday.