After a siege that began yesterday, the militants gained control of Marawi, a city of 200,000 in the south of the country.
President Duterte spoke publicly of how anyone who fought against the government would fare, saying, "You will die."
Duterte declared martial law in the south yesterday. He said he will extend martial law to the rest of the country if the militants expand.
Islamist militant communities have long been a problem for the Philippines, although mostly confined to the south.