German special Police walks near the main train station in Cologne, Germany, October 15, 2018, after the train station was closed after hostage-taking. REUTERS/Thilo Schmuelgen

BERLIN (Reuters) - The main train station in the western German city of Cologne has been closed due to an ongoing police operation, state-owned rail operator Deutsche Bahn said on Monday after police said they were investigating a suspected hostage-taking.

“A police operation is delaying rail traffic, the main station in Cologne is closed,” Deutsche Bahn said on Twitter, adding it did not know how long the police operation would last.