German authorities have arrested two brothers on suspicion of planning an attack on one of the country’s biggest shopping centres, in the western city of Oberhausen, according to police.

The two men, aged 28 and 31, are originally from Kosovo, they said. It was not clear if there was any connection with the attack on Berlin’s Breitscheidplatz on Monday night, in which a man drove a truck into a Christmas market, killing 12 people.

Special forces arrested the two men in the city of Duisburg after information provided by security sources, police said.

Investigators were trying to establish what stage of preparation the plot was at and whether others were involved, police in the nearby city of Essen said in a statement.

Tipped off by the intelligence services, police were sent to the shopping mall and a nearby Christmas market late on Thursday, they said.

The mall that was targeted, CentrO, is one of the largest in Germany, with about 250 shops that are usually packed in the run-up to Christmas. It is located in an old steelworks in Oberhausen in the former industrial heartland of the Ruhr valley.

Police were still hunting for a 24-year-old Tunisian, Anis Amri, the man suspected of carrying out Monday’s attack on one of the capital’s most popular Christmas markets.

Isis has claimed responsibility for the assault, which would be its deadliest yet carried out on German soil.

Agence France-Presse and Reuters contributed to this report.