MADRID: Spain's San Fermin festival, a heady mix of bull-runs and partying that wraps up Thursday, is under attack from women's groups who say it has a hidden record of sexual assaults.

And they accuse the muncipality of trying to cover up the issue.

A 22-year-old woman filed a police complaint for sexual assault Monday in a public toilet at a park by a man she had met at a bar in the northern city of Pamplona, according to two women's groups, “Andrea” and “Lunes Lilas”.

A 16-year-old girl was also raped during the weekend, they said.

The head of hospital emergency services for the region of Navarra, Javier Sesma Sanchez, confirmed that two women were treated for sexual assault during the festival and he said a third possible case was under investigation.

“That is the information which we have,” he told a news conference when asked how many cases of sexual assualt were recorded at San Fermin.

About 200 people of all ages, many wearing traditional white clothes with red bandanas around their necks, staged a silent protest outside Pamplona's baroque city hall on Monday night against sexual assualts.

Another protest is scheduled for before the final bullfight of the festival. It will be held outside Pamplona's bullring and it is organised by clubs of fans of the San Fermin festival known as “penas”.

“We have for years endured seeing how this festival is sold with the phrase: 'At San Fermin anything goes',” said Zurine Altable, spokeswoman for Pamplona's “Gora Irunea” collective.

“At San Fermin, as at any other festival, not everything is allowed. When a woman says 'no' she means 'no',” she added.

“We demand real information about the sexual assaults that take place at San Fermin. This is a reality that everyone knows and which Pamplona city hall and other institutions try to make invisible.”

Women's groups have set up a hotline for women to report attacks and have plastered the city with posters that read: “No to sexual assaults”.

Large banners bearing the same phrase in the Basque language hung from apartment buildings in the city centre.

“Acts like these need to be made public,” said Pamplona alderman Itziar Gomez. “You can not hide these things, the fiesta has both a white and a black side to it.”

Pamplona mayor Enrique Maya, who initially had made no comment on the reports of the sexual assualts, on Tuesday vowed a full investigation.

“If it is proven that these types of abuses took place, we will have to apply the law to its full extent,” he told reporters.

Festival turnout figures are not yet available but Pamplona officials predicted the city of some 200,000 residents would at least match last year's figure of 1.5 million people and a hotel occupancy rate of over 90 per cent.