Sydney - Australian police charged a top Vatican cardinal on Thursday with multiple counts of historical sexual assault offences, a stunning decision certain to rock the highest levels of the Holy See.Cardinal George Pell, Pope Francis' chief financial adviser and Australia's most senior Catholic, is the highest-ranking Vatican official to ever be charged in the church's long-running sexual abuse scandal. Pell said he would return to Australia to fight the charges.Victoria state Police Deputy Commissioner Shane Patton said police have summonsed Pell to appear in an Australian court to face multiple charges of "historical sexual assault offences," meaning offences that generally occurred some time ago. Patton said there are multiple complainants against Pell, but gave no other details on the allegations against the cardinal. Pell was ordered to appear in Melbourne Magistrates Court on July 18.Strenuously denying all allegationsFor years, Pell has faced allegations that he mishandled cases of clergy abuse when he was archbishop of Melbourne and, later, Sydney. But more recently, Pell himself became the focus of a clergy sex abuse investigation, with Victoria detectives flying to the Vatican last year to interview the cardinal. It is unclear what allegations the charges announced on Thursday relate to, but two men, now in their 40s, have said that Pell touched them inappropriately at a swimming pool in the late 1970s, when Pell was a senior priest in Melbourne.The Catholic Archdiocese of Sydney issued a statement on behalf of Pell, saying the 76-year-old cardinal "strenuously denied all allegations" and would return to Australia to clear his name."He said he is looking forward to his day in court and will defend the charges vigorously," the statement said.Patton told reporters in Melbourne that none of the allegations against Pell had been tested in any court, adding: "Cardinal Pell, like any other defendant, has a right to due process."The charges are a new and serious blow to Pope Francis, who has already suffered several credibility setbacks in his promised "zero tolerance" policy about sex abuse.Abuse historyPell's actions as archbishop came under intense scrutiny in recent years by a government-authorised investigation into how the Catholic Church and other institutions have responded to the sexual abuse of children.Australia's Royal Commission into Institutional Responses to Child Sexual Abuse — the nation's highest form of inquiry — has found shocking levels of abuse in Australia's Catholic Church, revealing earlier this year that 7% of Catholic priests were accused of sexually abusing children over the past several decades.Last year, Pell acknowledged during his testimony to the commission that the Catholic Church had made "enormous mistakes" in allowing thousands of children to be raped and molested by priests over centuries. He conceded that he, too, had erred by often believing the priests over victims who alleged abuse. And he vowed to help end a rash of suicides that has plagued church abuse victims in his Australian hometown of Ballarat.Australia has no extradition treaty with the Vatican. But in the statement from the Sydney Archdiocese, Pell said he would return to Australia "as soon as possible," following advice and approval by his doctors. Last year, Pell declined to return to Australia to testify for the third time before the Royal Commission, saying he was too ill to fly. He instead testified via video conference from Rome.The charges put Pope Francis in a thorny position. In 2014, Francis won cautious praise from victims' advocacy groups when he created a commission of outside experts to advise him and the broader church about "best practices" to fight abuse and protect children.But the commission has since lost much of its credibility after its two members who were survivors of abuse left. Francis also scrapped the commission's signature proposal — a tribunal section to hear cases of bishops who covered up for abuse — after Vatican officials objected.In addition, Francis drew heated criticism for his 2015 appointment of a Chilean bishop accused by victims of helping cover up for Chile's most notorious pedophile. The pope was later caught on videotape labelling the parishioners who opposed the nomination of being "leftists" and "stupid."When Francis was asked last year about the accusations against Pell, he said he wanted to wait for Australian justice to take its course before judging."It's true, there is a doubt," he told reporters en route home from Poland. "We have to wait for justice and not first make a mediatic judgment — a judgment of gossip — because that won't help.""Once justice has spoken, I will speak," he said.