Berlin police say some 900 officers have raided one of the German capital's biggest brothels and arrested six people following a months-long investigation into human trafficking, tax fraud and withholding of social security contributions.

Police said Thursday the raid at Artemis brothel late Wednesday was conducted by police officers as well as customs office employees and tax fraud investigators.

Prosecutors said that sex workers at Artemis were forced to pretend they're self-employed so their bosses did not have to pay social security contributions.

Police said that since the opening of the brothel in 2006, some 17.5 million euros ($19.7 million) in social security contributions had not been paid.