The Philippine military said on Sunday it had found the bodies of 16 civilians as troops tried to gain control over Marawi City, which has been under siege from ISIS-allied militants.

President Rodrigo Duterte announced Tuesday he was imposing a 60-day period of martial law in the southern Philippines. He also suggested he may expand it nationwide, saying "it would not be any different from what President Marcos did," referring to the country's longtime dictator, who declared martial law in 1972.

There have been Muslim separatists in the region for decades, but recently groups have been aligning with ISIS. The siege "seems to be an effort by ISIS-inspired local groups to be recognized as a province of their caliphate," reporter Michael Sullivan told NPR yesterday, and the Philippine government is now taking the threat posed by ISIS more seriously. "[O]fficials said there were foreign fighters among the militants killed so far. So it's clear it's not just homegrown anymore."

Eight bodies were found in a ravine on the outskirts of Marawi City. "The men were executed on the road above, the police commander on the scene said," Sullivan told NPR's Newscast. "Bloodstains on the side of the road--and nine spent bullet casings in his hand--seemed to back up his theory."

Marawi is a mostly Muslim city of 200,000 is on the island of Mindanao. Most residents of the city have fled, but the AP reported that more than 2,000 were still trapped in the city. The wire service said that many of those trapped sent text messages pleading for rescue. "Have mercy on us, we don't have any more water to drink," read one.

The military offensive began on Tuesday, when the government tried to capture Isnilon Hapilon, a senior leader with Abu Sayyaf, a gang that kidnaps for ransom. Hapilon is on the FBI's Most Wanted Terrorists list; the U.S. has offered a $5 million reward for his capture.

But the military was surprised by jihadi fighters, and the militants have dug in. The military says the death toll since Tuesday is close to 100, the AP reports. That figure includes 16 civilians, 61 militants, 11 soldiers, and four police officers.

"In as much as we would like to avoid collateral damage, these rebels are forcing the hand of government by hiding and holding out inside private homes, government buildings and other facilities," military spokesman Brigadier-General Restituto Padilla said, according to The Guardian.

"Their refusal to surrender is holding the city captive. 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."

On Friday, Duterte visited troops in Iligan City. While there, he said that he'd take responsibility for the consequences of soldiers enforcing martial law, joking that soldiers could rape women with impunity.

"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 jobs," he said, according to The New York Times. "I will go to jail for you. If you raped three, I will own up to it."

As The Guardian reported, this is not Duterte's first public joke about rape:

"He caused outrage in the lead-up to his presidential election win last year when he recalled a 1989 prison riot in which an Australian missionary was killed, and inmates had lined up to rape her.

"In what was intended as a joke, Duterte said the victim was 'beautiful' and as mayor of Davao city where the riot took place, he should have been first in line. He later apologised and said he did not intend to disrespect women or rape victims.

"Duterte's speeches are often loaded with profanity, threats and jokes about taboo subjects, which offend some, but are taken lightly by many Filipinos."

Last month, President Donald Trump invited Duterte to visit the White House.

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