German police in four states arrested nearly 100 people in brothel raids during a crackdown on illegal prostitution ahead of next month's World Cup.

Police in Hesse, Rhineland-Palatinate, Baden-Wuerttemberg and Bavaria questioned hundreds of sex workers in the statewide raids, authorities said Thursday.

Volker Bouffier, interior minister of Hesse, said the raids Wednesday were launched in an effort to combat concerns expressed by human rights organizations and other groups that thousands of women, mostly from Eastern Europe, could be smuggled into Germany and forced to work as prostitutes during the World Cup. The monthlong event starts June 9.

"The controls and searches are an effective way to fight against such crimes, and for this reason (we) will continue to carry out such actions," Bouffier said.

Police in Hesse checked the documentation and registration of 603 prostitutes, making 74 arrests. Authorities in neighboring Rhineland-Palatinate said they arrested 22 people and another 34 were issued citations, mostly for immigration violations and failure to comply with business regulations.

Prostitution is legal in Germany and sex workers, who pay taxes and receive social benefits, are required to register with authorities. About 400,000 people are registered in the trade.

No information was immediately available on the results of the searches in Baden-Wuerttemberg and Bavaria.

Human rights groups including the Council of Europe, Amnesty International, the International Organization for Migration and the Angel Coalition, an anti-trafficking women's group in Russia, have called on Germany to be vigilant in the fight against human trafficking and forced prostitution during the World Cup.

About 3.5 million visitors are expected to attend the event.