Paris - French police questioned soccer internationals Franck Ribery and Karim Benzema on Tuesday as part of an investigation into an alleged under-age prostitution ring, a legal source said.

The footballers were detained at the request of an investigating magistrate probing allegations that a Champs Elysees nightclub provided clients access to minors working as call girls, the source close to the inquiry said.

One of the young women who is alleged to have met clients at the club had already testified to investigators earlier in the year that she had relations with the two players when she was still under age.

If they are charged and convicted of soliciting and paying for sex with a minor, the pair face three years in jail and a fine of 45 000 euros ($58 000), but only if it is proved they knew she was under-age.

A grim-faced Ribery arrived at the headquarters of the Paris vice squad with an acquaintance but refused to answer questions from reporters.

Boulogne-born 27-year-old midfielder Ribery plays for Bayern Munich in Germany and was a member of France's ill-fated squad at this month's 2010 World Cup in South Africa, which went out in the first round.

Real Madrid striker Benzema is only 22, but missed out on this year's French team, despite playing in much of the World Cup qualifying campaign.

Ribery has previously confirmed to police that he had sex with the young woman, but insists he did not know she was a minor. Benzema has not publicly addressed the allegations.

The young woman, Zahia Dehar, is now 18 years and four months old. She has been questioned by police and gave a tell-all interview to the news and gossip weekly Paris Match after the scandal erupted.

She described selling sexual encounters to Ribery in 2009 and to Benzema in 2008, while she was under-age, and with a third French player, 30-year-old Panathinaikos winger Sidney Govou, in March, when she was an adult.

Dehar has also said the players did not know she was a minor. In France the general age of consent is 15 years, but in the case of prostitution a young person remains a minor until he or she reaches 18.

The footballers became caught up in the investigation after detectives probing rumours of a vice ring bugged the Zaman Cafe, an expensive nightspot just off Paris's most glamorous street, the Champs Elysees.