Philippine President Rodrigo Duterte was heavily criticized on Saturday for a joking about soldiers raping women as they enforced martial law.

Duterte jokingly told soldiers in the country's south on Friday they were allowed to rape up to three women. 

"I will be imprisoned for you. If you rape three (women), I will say that I did it. But if you marry four, son of a whore you will be beaten up," he said.

Duterte was speaking in a military camp in Mindanao island, parts of which have been under martial law since Tuesday following an attack by Islamist militants.

Duterte said he intended the remark as "a joke," reiterating that only he would be liable for any backlash over military rule.

"If you go down, I go down. But for this martial law and the consequences of martial law and the ramifications of martial law, I and I alone would be responsible, just do your job, I will take care of the rest," Duterte said on Friday, according to a president's office transcript.

'Sickening attempt at humor'

Phelim Kine, a deputy director with Human Rights Watch's Asian division, described the joke as a "sickening attempt at humor".

He and Filipino rights activists warned the joke signaled to soldiers that they could commit rights abuses as they enforced martial law.

"Duterte's pro-rape comments only confirm some of the worst fears of human rights activists that the Duterte government will not just turn a blind eye to possible military abuses in Mindanao, but may actively encourage them," Kine said.

Gabriela, a women's political party in the Philippines, also expressed outrage.

"Rape is not a joke. Martial law and the heightened vulnerability to military abuse that it brings to women and children are not a joke either," it said in a statement.

"Not funny. Ever," wrote Chelsea Clinton, the daughter of ex-US president Bill Clinton and former secretary of state Hillary Clinton, on Twitter.

"Duterte is a murderous thug with no regard for human rights. It's important to keep pointing that out & that rape is never a joke."

Duterte's spokesman, Ernesto Abella, said Duterte was using "heightened bravado" when trying to raise the morale of the troops.

"He gave his full support to the men and women in uniform, taking complete responsibility for their actions, even exaggeratedly describing crimes like taking a fourth wife," Abella said in a statement, while ignoring Duterte's preceding rape remark.

Duterte imposed 60 days of martial law in the southern third of the country when a group aligned with the so-called "Islamic State" launched raids on Marawi, a city of 200,000 people.

Attacks on first day of Ramadan

On Saturday, the first day of the holy month of Ramadan, Philippine military forces attacked suspected positions of the Islamist militants.

Troops have conducted artillery strikes and "surgical strikes" on militant positions.

"We will try our best to clear the area at the soonest possible time," Lieutenant General Carlito Galvez, a regional military commander, told reporters in Marawi. "We apologize to our Muslim brothers for interfering with the first day of Ramadan."

"We are using maximum power to really make them withdraw so that we can normalize the situation," he said. "We need to drive them away so that we can protect our interests here." Brigadier General Restituto Padilla said the militants were "hiding and holding out inside private homes, government buildings and other facilities."

"Their refusal to surrender is holding the city captive," he said in a statement.

"Hence, it is now increasingly becoming necessary to use more surgical airstrikes to clear the city and to bring this rebellion to a quicker end."

Communist peace talks break down

The imposition of martial law led to a breakdown in peace talks with unrelated communist separatists. 

Communist insurgents, who are active in wide areas of the archipelago, including the south, responded to Duterte's declaration of martial law by ordering their forces to "carry out more tactical offensives".

Negotiators for the communist alliance negotiators said the directive came after government officials announced that New People's Army fighters would also be targeted in Manila's crackdown on Islamic extremists.

Manila's negotiators suspended the peace talks following the call to arms.

aw/kl (AFP, Reuters, AP, dpa)