The front-runner in the Philippine presidential race apologized Tuesday for a campaign rally remark about wanting to rape an Australian missionary who was assaulted and killed by prisoners during a hostage-taking in 1989.

The comment by Mayor Rodrigo Duterte of southern Davao city sparked a storm of criticism ahead of the May 9 election.

Duterte issued an apology saying "sometimes my mouth can get the better of me" and adding that he has "no intention of disrespecting our women and those who have been victims of this horrible crime."

At a campaign stop last week, Duterte said he "should have been the first" to rape Australian Jacqueline Hamill, whose throat was slit by prisoners after she was raped during a 1989 prison siege. His supporters laughed and cheered at the comment.

Rival candidates and women's groups, however, were shocked and slammed the tough-talking mayor for the remark. A rival candidate for the presidency called Duterte a "crazy maniac" who is not fit to lead the nation.

Australian Ambassador Amanda Gorely tweeted Sunday that "rape and murder should never be joked about or trivialized" and "violence against women and girls is unacceptable anytime, anywhere."

An incensed Duterte asked Gorely to "shut up," according to news reports.

Duterte's campaign promise to rid the Philippines of criminals, drug dealers and corrupt politicians in six months has won him wide support but political analyst Ramon Casiple said his rape remark may alienate the undecided whose backing may be crucial in the tight contest among four contenders.

Duterte was in the lead in a voter preference survey conducted days before his comment.

"It can possibly be his Waterloo," Casiple said. "There's not much time. It remains to be seen whether corrective measures by his camp can still gain traction."

Duterte has come under fire for past remarks. Last year, he cursed Pope Francis for causing a traffic jam during a visit to Manila that trapped the mayor for hours.

Stunned Roman Catholic bishops criticized the mayor, who later said he was sorry and wrote a letter of apology to the pope.