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BERLIN, Germany — A carnival parade in the northern German town of Braunschweig was cancelled at short notice Sunday due to a "concrete threat" of an Islamist attack, police said.

"Reliable state security sources have made it known that a concrete threat of attack with an Islamist background exists," authorities in Braunschweig said in a statement.

Police called on all visitors to refrain from visiting the planned route of the carnival parade and avoid travelling to Braunschweig.

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According to a police spokesperson, the carnival parade was cancelled following a specific "threat assessment." The officials would not provide specific information about the type of threat, but said that the inner city "was searched with explosives search dogs."

Similar to many other smaller German cities, the Sunday carnival parade was due to run through the city center. In Braunschweig, approximately 200,000 to 250,000 people visit the 'Fastnacht' parade with its traditional floats every year.

A police spokesperson told NBC News that an investigation is underway and that federal authorities are involved. On Monday, the cities of Duesseldorf, Cologne and Mainz will see the main German carnival parades, which regularly draw millions of visitors in these Rhineland cities.

The cancellation came after two civilians died and five policeman were wounded in attacks in Denmark on Saturday at an event promoting freedom of speech and on a synagogue.

Police officers secure the city center of Braunschweg, Germany. PETER STEFFEN / EPA

IN-DEPTH

— Andy Eckardt

Reuters contributed to this report