MANILA - Sen. Pia Cayetano is not amused by PDP-Laban standard-bearer Rodrigo Duterte's joke about the rape of an Australian missionary.

Cayetano, sister of Duterte's running mate Sen. Alan Peter Cayetano, said her stand on gender issues has not changed. The female Cayetano is the chairwoman of the Senate Committee on Women, Children, Family Relations and Gender Equality and is best known for pushing the passage of the Responsible Parenthood and Reproductive Health Act of 2012 (RA 10354) and the Expanded Breastfeeding Promoting Act (RA 10028).

"My stand on gender issues doesn't change. Joking about rape is not funny. As I said, I've reached out to Mayor [Duterte] and his team," she said.

My stand on gender issues doesnt change. Joking about rape is not funny. As I said, I've reached out to Mayor and his team.

— pia cayetano (@piacayetano) April 17, 2016

Rest assured I always take these issues seriously. May not be able to respond to tweets but I'm dealing with it.

— pia cayetano (@piacayetano) April 17, 2016

Duterte, whose campaign promises a ruthless war on crime, was angrily condemned on Sunday after a video of him joking about a murdered Australian rape victim surfaced.

Duterte, who promises to reduce criminality and corruption in 3 to 6 months if elected, appears in the video making a joke about the female Australian missionary.

The missionary, who was ministering in a prison in Davao in the southern Philippines, was allegedly raped and killed during a riot by inmates in 1989.

Duterte was the city mayor at the time.

"They raped all of the women... There was this Australian lay minister... when they took them out... I saw her face and I thought, 'Son of a bitch. what a pity... they raped her, they all lined up. I was mad she was raped but she was so beautiful. I thought, the mayor should have been first," Duterte is shown telling a crowd of laughing supporters at a campaign rally.

Duterte, who boasts of extra-judicial killings of crime suspects by vigilantes during his time in Davao, is the leading candidate in the run-up to the May 9 election, according to the latest opinion survey of ABS-CBN conducted by Pulse Asia.

His rivals, women's groups and commentators on social media quickly denounced his remarks.

President Benigno Aquino's spokesman Herminio Coloma said the comments show "his lack of fitness for the presidency" and his "utter lack of respect for women."

Aquino, who under the constitution cannot seek a second term, is supporting another candidate, his former interior secretary Mar Roxas, who trails Duterte in opinion surveys.

Rival presidential candidate Vice President Jejomar Binay called Duterte's remarks "simply revolting."

"You are a crazy maniac who doesn't respect women and doesn't deserve to be president," Binay told Duterte in a statement.

Another candidate Senator Grace Poe, who is just behind Duterte in the surveys, called his comment "distasteful and unacceptable, and reflects his disrespect for women."

One Filipino remarked on Twitter: "I broke down after watching Duterte on Aussie rape. I can't fathom how his followers can laugh at it."

Women's group Gabriela attacked Duterte's remarks, saying rape or any other form of sexual abuse was not a joke "nor something to be trivialised in a joke," especially by someone seeking the presidency.

Many Filipinos have embraced Duterte for his vulgarity-laced speeches, his boasts of sexual conquests and his promised war on crime.

Even when he called Pope Francis a "son of a whore," in a speech last November, his followers in the devoutly Catholic nation quickly forgave him.

Spokesmen for Duterte had no immediate comment when approached by AFP. Many of his followers brushed off the controversy.

"We won't apologize for he has done nothing wrong, it was a clear joke for God's sake," one Filipina supporter said on Twitter. With Agence France-Presse