Criminal gangs from Turkey and Iraq were responsible for smuggling Iraqi Kurds aboard a freighter that ran aground in France, police said.
Police said "an Iraqi-Turkish mafia ring" brought 910 people on the boat.
Officers know the captain's name and are working with Interpol to find him and the ship's owner.
Police director Daniel Chaze said those willing to pay 200-300 dollars were taken to the Turkish border. A Turkish smuggling ring then loaded the refugees onto the freighter for the week-long voyage by sea.
The refugees were charged up to 2,000 dollars each for the trip, even though they had no idea where they were going.
About 150 Red Cross officials have been dispatched to a military camp where the refugees were given temporary shelter.
Eric Painsec, head of aid operations for the French Red Cross, said most were in satisfactory health, although many suffered from fatigue.
Magjid Salah, 65, paid 10,000 dollars to travel with his family of nine, including his 100-year-old mother.
"From Iraq, we went into Turkey about two weeks ago. We were locked up in a truck. We didn't know where we were going and if it was day or night."
Ismail, a 30-year-old Iraqi Kurd who travelled with his wife and three children, said the refugees were kicked and threatened while on board. He declined to give his last name.
"I want to go where there is democracy. I would rather die than go back there."