Prosecutors at Spain's top criminal court opened a preliminary investigation Monday into Spanish football chief Luis Rubiales' forcible kiss on the lips of World Cup player Jenni Hermoso on grounds it could constitute a crime of "sexual assault".

The Spanish football federation (RFEF) regional presidents then asked the 46-year-old to resign because of his "unacceptable behaviour" and called for "profound and imminent" restructuring of the organisation.

The RFEF statement leaves Rubiales shorn of allies -- some of the regional presidents had been among those who applauded his speech last Friday, in which he insisted he would not resign, and his kiss was "consensual", contested by Hermoso.

Spain's National Court said they had opened a preliminary probe into Rubiales's kiss on Hermoso at the World Cup final in Sydney on August 20, "which could constitute an offence of sexual assault".

They would also contact Hermoso to offer her a chance to file a lawsuit within 15 days, the court statement said.

After Spain won the Women's World Cup Rubiales sparked a massive backlash with his unsolicited kiss during the medal ceremony.

Hermoso later said the incident left her feeling "vulnerable and like the victim of an assault", with a statement on social media describing it as "an impulsive, macho act, out of place and with no type of consent on my part".

The National Court said it was opening the investigation in light of the "unequivocal nature" of her statements, saying it was necessary "to determine their legal significance".

"Given the public statements made by Jennifer Hermoso, the sexual act she was subjected to by (Luis) Rubiales was not consensual," the court statement said.

"In order to proceed with a case for sexual assault, harassment or sexual abuse, it will be necessary for the injured party or their legal representative to file suit."

If Hermoso decides not to file a complaint, it will make it "difficult" for prosecutors to press ahead with the case, legal sources told AFP.

- Resignation request -

World football governing body FIFA provisionally suspended Rubiales for 90 days last week while they open disciplinary proceedings against him -- but the president may have resigned before that if he heeds the request from the RFEF's 19 regional presidents.

"After recent events and the unacceptable behaviour that has seriously damaged the image of Spanish football, the presidents request that Luis Rubiales resign immediately as president of the RFEF," the federation said following a meeting Monday.

The presidents said they backed interim chief Pedro Rocha, who convened the meeting between the regional presidents, to lead the organisation into "dialogue and reconciliation with all football institutions".

The RFEF also urged an overhaul in the federation's management.

"We will urge the relevant authorities to carry out a profound and imminent organisational restructuring in strategic positions of the federation in order to make way for a new stage in the management of Spanish football," it read.

The regional presidents also congratulated the women's team on their World Cup triumph.

Presently 81 players, including Hermoso, are on strike, until the federation's leadership changes.

Their triumph has been "tarnished" by Rubiales' behaviour, according to Spanish football great Andres Iniesta.

Reports in Spain said RFEF general secretary Andreu Camps had reported interference from the Spanish government in sporting matters to UEFA -- something which contravenes the European football governing body's regulations and threatened La Liga club's involvement in continental competition.

The apparent purpose was to pressure the government, who are looking to issue their own suspension on Rubiales into backing down.

Criticism from the world of football and far beyond has not stopped mounting.

The spokesman for the United Nations secretary-general on Monday pitched into the sexism row engulfing Spain, asking: "How difficult is it not to kiss somebody on the lips?"

Stephane Dujarric, spokesman for UN chief Antonio Guterres, called on authorities to address sexism "in a manner that respects the rights of all female athletes"

With Rubiales under heavy fire, his mother Angeles Bejar locked herself in a church in the southern seaside town of Motril, and went on hunger strike in protest against the treatment of her son.