Philippine President Rodrigo Duterte has declared martial law for 60 days on the island of Mindanao, after clashes between the army and militants linked to so-called Islamic State (IS).
The violence on the southern island left three members of the security forces dead, officials say.
Mindanao is home to a number of Muslim rebel groups seeking more autonomy.
Mr Duterte made the announcement during a visit to Russia, which he was forced to cut short.
Martial law allows the use of the military to enforce law and the detention of people without charge for long periods.
The Philippine constitution says a president can only declare martial law for 60 days to stop an invasion or a rebellion.
Parliament can revoke the measure within 48 hours while the Supreme Court can review its legality.