French officials on Wednesday urged women to report any cases of sexual assault during the celebrations of France's World Cup win, after dozens of accounts by victims emerged on social media.

"These cases must be brought to our attention so that investigations can be carried out," Paris police chief Michel Delpuech said on Europe 1 radio.

"Our services will obviously pursue any aggressors without fail if they are identified," he said.

Reports of forced kisses and groping began appearing on Twitter after France won the final against Croatia on Sunday night, when hundreds of thousands of fans poured onto the streets of Paris and other cities.

Others recounted sexual assaults during other World Cup matches or at the team's victory parade in the Champs Elysees avenue on Monday.

Eventually people began using the hashtag #MeTooFoot, a nod to the Me Too movement that sprang up in the wake of rape and assault claims against Hollywood mogul Harvey Weinstein.

One 20-year-old student who was on the Champs Elysees on Sunday night when "a man came up behind me, I felt his hands on my bottom, then he grabbed my crotch."

"Today when I think of the final, I can't think of anything else," she told AFP.

Two people have been detained over suspected sexual assaults in Paris, including a minor, a judicial source told AFP.

It remained unclear, however, if there was an increase in the number of assaults linked to the World Cup crowds.

According to the interior ministry, the number of rape claims filed with the Paris police on Monday was half the number reported on the same date last year.

No increases in claims were noted in any other large cities, it added.

'We won, give me a kiss'

France's Equality Minister Marlene Schiappa has also urged victims to come forward, saying on Twitter on Tuesday: "A man forcibly kisses a woman during the World Cup parties, that's sexual assault that is punished by the law."

But several of the women posting #MeTooFoot accounts said they saw little reason to put their hope in the authorities.

A woman using the handle Dame en Noir (Lady in Black) posted Monday that a man unzipped his pants and began masturbating against her leg at a fanzone in Nantes, western France.

"I told the police but they said they were there in case of terror attacks," she wrote.

Rose also said she had not filed charges. "There's no point, because they'll never be able to find them," she said.

Rights activists noted that assault risks rise for women at nearly every big festival or street party, in particular when alcohol is flowing freely.

"Women can't party in public the way men do," said Raphaelle Remy-Leleu of the advocacy group Osez le Feminisme (Dare to Be Feminist).

She herself was a victim after France's semi-final win over Belgium, when a man grabbed her by the neck and started touching her crotch and trying to kiss her.

"He ended up with my fist in his face," Remy-Leleu said.

For Anne-Cecile Mailfert, president of the Women's Foundation, the dozens of postings show that the Me Too movement has had a lasting impact.

"We don't let this stuff go anymore," Mailfert said, though she added that more progress was needed.

"That's what we're seeing in some tweets by men saying, 'We won, give me a kiss'."

She called on officials to put more effort into preventing assaults at sporting events, for example with public announcements similar to a British campaign which warned about higher incidents of domestic abuse during the World Cup.