Here is what we know about why he declared martial law and what happens next:
What happened to trigger martial law?
Duterte acted after security forces on Tuesday battled dozens of gunmen in Marawi, a city of about 200,000 people. One policeman and two soldiers died in the fighting, authorities said.
Tuesday’s violence was the latest in a series of deadly clashes with militants who have pledged allegiance to the IS, and are based throughout Mindanao.
Duterte’s declaration fulfilled an often-repeated promise to impose martial law to combat the IS-linked militants, whom he has said are a growing threat to national security.
Who are the militants?
Authorities said they were battling members of two of the best-known groups to have declared allegiance to IS, the Abu Sayyaf and Maute organizations.
The military said it was hunting Isnilon Hapilon, an Abu Sayyaf leader who has been named the Philippine head of IS. The US government is offering a $5-million bounty for his capture.
The Abu Sayyaf is infamous for kidnapping foreigners and killing them if ransoms are not paid. It is also blamed for the nation’s worst terror attacks, including the 2004 bombing of a ferry in Manila Bay that claimed more than 100 lives.
The Jakarta-based Institute for Policy Analysis of Conflict said last year that deepening cooperation among the Maute gang, the Abu Sayyaf and other pro-IS groups meant more deadly violence was “a matter of when, not if.”
What will happen under martial law?
Martial law allows the president to “call out the armed forces to prevent or suppress lawless violence, invasion or rebellion,” according to the Constitution.
Defense Secretary Delfin Lorenzana said security forces would be able to arrest suspected militants and hold them. They will be released if they have not been charged within three days.
What happens next?
The Constitution limits martial law to 60 days unless Congress agrees to extend it.
The post-Marcos Constitution imposed safeguards on martial law, including the requirement for Congress to approve its imposition and extension. The Supreme Court can also rule on its legality.
(Agence France Presse)