PARIS - Nearly two dozen people went on trial Wednesday in the French city of Lyon for what activists say is an all-too-common reality in Europe: allegations of forced prostitution involving migrant women.

The 23 defendants face up to 10 years in prison if found guilty of a slew of charges, ranging from money laundering to human slavery. They are suspected of running a sex-trafficking ring that turned Nigerian women hoping for better lives in Europe into sexual slaves.

Those on trial include a Nigerian pastor, accused of being the ring leader, and a woman suspected of recruiting Nigerian women as prostitutes in Lyon and two other French cities. She is on the run and being tried in absentia.

Lawyers speak in the courtroom prior to the start of a trial of a prostitution network case in Lyon, France, Nov. 6, 2019.

Prosecutors say the 17 alleged victims earned about $160,000 per month for their masters selling cheap sex. Most came from the same area — Benin City in southern Nigeria, a pattern seen in Italy and elsewhere in Europe, experts say.

"It's a business and there is money ... and Nigerians at the moment are one of the most efficient traffickers," said Helene de Rugy, a senior member of French NGO L'Amicale du Nid, which joined the prostitutes as a plaintiff in the case.

Most of the sex workers stayed away from the trial for fear of reprisals — something de Rugy said happened last year during a similar sex trial in Lyon.

Police say Nigerians make up a large portion of France's prostitute population. De Rugy says it reflects a wider European phenomenon, although it's hard to put exact figures to its size.

"Victims are transported from one country to another. We even meet victims who don't know [in] which country they are," she said.

De Rugy says France must do more to crack down on prostitution and to protect the victims. So must Nigerian authorities, she says — by stepping up the fight against female trafficking at home.

