Philippine President Rodrigo Duterte has warned he would deal harshly with militants following his declaration of Martial Law on Mindanao island, after a failed raid on a hideout of rebels linked to the Islamic State group ISIS.

Duterte called a halt on his Moscow trip after news of the clash broke out in Marawi City, Lanao del Sur in Mindanao. Shortly after, the 16th president of the Philippines had fulfilled his warning four days prior, in a May 19 speech at the 33rd Philippine Coast Guard Auxiliary National Convention held in his hometown, Davao City.

Maute lays siege

On Tuesday, members of the rebel group Maute took over the Amai Pakpak Medical Center, with the group reportedly replacing the Philippine flag with a black flag, supposedly representing the Islamic State. Residents said they saw the black banner of the terrorist Islamic State mounted on vehicles on the streets of Marawi as the fighting raged.

Armed Forces of the Philippines (AFP) First Infantry Division Spokesman Lt. Col. Jo-Ar Herrera reported rebels took the streets of Barangay Basak Malutlut at 2 p.m. According to the report, the firefight arose after government troops attempted to apprehend Isnilon Hapilon, leader of the Abu Sayyaf. Hapilon, 51, whose hideout in Marawi City was targeted by Philippines troops Tuesday, is on the FBI’s “most wanted terrorist” list, with a $5 million reward for his capture.

Duterte: ‘Do not force me’

Duterte had mentioned martial law at least a dozen times since October 2015, or a month before declaring his aims for the presidential seat.

He is primarily known for his iron-fist rule in Davao City, where he served as mayor for more than two decades.

The military’s most recent report indicated at least 13 members of Maute were killed in the ongoing clearing operations. Out of 13 fatalities, only two bodies were recovered. Meanwhile, 31 soldiers have been wounded, and among those unfortunately killed were five members of the AFP and two police officers.

Meanwhile, the military’s spokesman said government security forces are continuing their operations in Marawi City in a bid to finish alleged ISIS representative Hapilon and his cohorts.

Duterte declared martial rule for 60 days in the entire Mindanao region, home to 22 million people. “I warned everybody not to force my hand into it,” he said on his plane en route to the Philippines. “I have to do it to preserve the republic.”