"I had no choice. They are destroying Marawi. I have to drive them out. But I am very sorry," Duterte said. He was speaking at a makeshift evacuation center for hundreds of residents of the northern Mindanao city who have been forced to flee their homes.
"I will rebuild Marawi," he promised.
The battle has resulted in numerous deaths and triggered a humanitarian crisis in the country. According to the Philippines government, more than 330,000 people have been forced to flee their homes.
The majority have found shelter with friends and family, but more than 16,000 internally displaced people (IDPs) are crowded into evacuation centers, where government agencies are trying to provide basic necessities.
One temporary resident at the camp, 70-year-old Gute Umpa, said he didn't know when they would be able to return to their homes -- and if they would still be standing when they did.
"I'm afraid our homes and properties have been turned to ashes and nothing can be retrieved or reused," he said.
"It's appalling that they would strike during Ramadan. Because of what happened, we cannot celebrate Eid."
'Dogs of hell'
Datu Abul Khayr Alonto, former mayor of Marawi, Moro National Liberation Front leader and current chairman of the Mindanao Development Authority, gave a fiery speech ahead of Duterte's address in Iligan, a city about 40 kilometers (25 miles) from Marawi.
"Your government, the president of Philippines, Rodrigo Duterte did not declare war against the good people of Marawi," he told the crowd of invited guests and IDPs. "He didn't burn your own homes."
The coalition of Mindanao-based militants have held territory in the Muslim-majority Philippines city for over a month, and Alonto warned against their message.
"They will come to you with beautiful language, they will even read the Koran to you... but don't touch them because they are the dogs of hell," he said.
Last week, Froilan Gallardo, a journalist with Mindanao-based Minda News, told CNN Marawi, a once-thriving city of about 200,000 people, is now a "ghost town."
Only a handful of residents remain, he said, and large areas of Marawi, especially the downtown commercial district, are "devastated" by the government bombardments.
Military casualties continue to mount, despite daily bombardment of areas controlled by insurgents in the city.
As of June 17, 56 government troops have been killed in action.
Lt. Colonel Jonna Dalaguit, the head doctor at a military hospital in the region, told CNN her facility had treated more than 340 wounded troops throughout the fighting.
Philippines soldiers have been mired in grinding urban warfare with ISIS-aligned fighters ever since a surprise attack on Marawi on May 23 -- the first instance of disparate, ISIS-aligned Filipino groups banding together and holding territory.
Militants stormed the city, clashing with government troops and prompting Duterte to declare martial law in Mindanao. The siege unfolded as Muslims worldwide began to mark the holy month of Ramadan. While the Philippines is predominantly Catholic, Mindanao has a sizable Muslim population.
The attack was endorsed by ISIS, whose media wing, Amaq Agency, put out a statement announcing that "fighters of the Islamic State launch a wide-scale offensive on positions of Philippine troops in the city of Marawi."
Philippines Armed Forces operations continue but have not been able to yet dislodge a core group of militants, led by Isnilon Hapilon, the leader of the Abu Sayyaf terrorist group, who was declared the emir of Southeast Asia by ISIS' leader, Abu Bakir al-Baghdadi.
The military claims to have killed at least 242 militants, but say the fighters continue to hold on to at least four neighborhoods in the heart of the city.
As the fighting wears on, deadline after deadline set by the Philippines government for the end of the conflict has been missed, including a pledge to finish the fighting by June 12, the country's Independence Day.
The fighting has also led to Duterte reversing the country's position on international military cooperation
. Less than a year after the president unambiguously declared that he did not want to "see any military man of any nation" in the Philippines "except the Filipino soldier", his spokesman announced that the country is open to assistance from other countries, if they offer it.