The situation in the south became more tense Wednesday after the Roman Catholic Church said gunmen had taken a priest and several churchgoers hostage in the city of Marawi as fighting raged between government forces and militants.
Mr. Duterte, speaking earlier in a video message released by his communications team, sought to calm public fears, even as he compared his imposition of martial law to that of the strongman Ferdinand Marcos, who subjected the entire country to martial law in the name of fighting communism.
“It would not be any different from what President Marcos did,” Mr. Duterte said in the video. “I’d be harsh.”
His spokesman said on Tuesday night that martial law would last only 60 days, but Mr. Duterte said he was prepared to extend it to a year.
His statement came as government forces were trying to quell fighting in Marawi, a city of about 200,000 that has become a hotbed of Islamist militancy.
The National Union of Peoples’ Lawyers in Manila said it was raising “serious concerns on what appears as a sledgehammer, knee-jerk reaction” to the situation on Mindanao.
“The recent incidents in Marawi do not justify the shotgun declaration of martial law,” said Ephraim Cortez, head of the lawyers’ union. “The declaration of martial law should be an option of last resort.”
Marcos ruled the country for two decades, much of it under martial law, leading to widespread human rights abuses and extrajudicial killings. He was forced into exile in Hawaii in 1986 after his government was toppled by the so-called People Power Revolution. He died in exile in 1989.
Sporadic violence continued on Wednesday in Marawi, as insurgents burned down the Catholic church where the hostages were abducted and set fire to at least two other buildings. They also hoisted a black Islamic State flag in the area.
Bishop Edwin de la Peña said the gunmen were holding at least six people, including the priest. He said a man who identified himself as one of the gunmen called him and demanded that government troops stop their search for the rebel leader.
“The man on the phone identified himself as one of the leaders of the armed group who confirmed holding hostage” the priest and others, Bishop de la Peña said. He added that the man warned they would harm the hostages if the troops and the police did not pull back.
But as Mr. Duterte was warning about the dangers of Islamist militancy, his own military was playing down the threat from the Islamic State.
Col. Edgard Arevalo, a military spokesman, said the situation in Marawi had “stabilized” with security forces in full control. He said the armed men were “not ISIS” but members of a local terrorist group.
“The news being circulated by these terrorists and their sympathizers are spurious and are meant to spread lies and disinformation,” he said. “It is propaganda to attract foreign terrorists’ support and recognition.”
The military said earlier that it launched the operation against the rebels with the police on Tuesday night in hopes of arresting Isnilon Hapilon, a leader of the Abu Sayyaf group, who was reportedly in the area and had been joined by an additional 100 militants belonging to a group called Maute.
Both groups have pledged allegiance to the Islamic State and vowed to carry out attacks across the Philippines, Asia’s center of Catholicism.
Abu Sayyaf has long targeted both locals and foreigners in the region. The group beheaded a German hostage this year and killed two Canadians in 2016.
Thirty-seven members of Maute, including a Malaysian and three Indonesians, were killed last month in clashes, also in the south.
Mr. Hapilon, a senior Abu Sayyaf leader, is considered one of the most radical members of the group. He pledged allegiance to the Islamic State in videos circulated online last year.