PARIS—French police on Monday detained Uber Technologies Inc.’s top two executives in Paris, French prosecutors said, making good on the government’s promise to crack down on the car-hailing service after violent protests by taxi drivers last week.

Investigators for the French police’s online-fraud unit are questioning Pierre-Dimitri Gore-Coty, Uber’s general manager for Western Europe, and Thibaud Simphal, Uber’s general manager for France, a spokeswoman for the Paris prosecutor’s office said Monday.

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