Foreign jihadists have been fighting with local militants in the southern Philippines in an "invasion" aimed at establishing a caliphate of the Islamic State in the country, officials say.
Six of 31 militants killed in the military offensive to secure the besieged city of Marawi were foreigners whose nationalities were still being verified, military spokesman Lieutenant Colonel Restituto Padilla said on Friday.
"There are certain foreign elements who have been in the country for a long time aiding these (local) terrorists," he said.
Militants from Indonesia, Malaysia and Singapore were among the jihadists fighting with local militants from a group called Maute in Marawi, Solicitor-General Jose Calida said.
"What's happening in (the southern region of) Mindanao is no longer a rebellion of Filipino citizens," Calida told a news conference.
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"It has transmogrified into an invasion by foreign terrorists who heeded the clarion call of the IS to go to the Philippines if they find difficulty going to Iraq or Syria."
Isnilon Hapilon, the wanted leader of another local terrorist group called Abu Sayyaf, was "declared by the IS as its emir or leader in the Philippines", Calida said.
President Rodrigo Duterte declared martial law in Mindanao on Tuesday because of these threats.
Duterte has also threatened to expand its reach to the entire country if the threat spreads.
Hostilities in Marawi erupted on Tuesday after government forces tried to serve an arrest warrant against Hapilon.
The country's military chief says Hapilon is still in the city.
"Right now, he is still inside (the city)," General Eduardo Ano told the Associated Press.
"We cannot just pinpoint the particular spot."
He said militants are trying to find a way to extricate Hapilon.
Aside from 31 militants, 15 soldiers, police officers and civilians have also been killed in the hostilities.
The militants burned two schools, a Catholic church, the city jail and several houses, beheaded a police chief and took a priest and an undetermined number of civilians hostage.
Thousands of residents have fled Marawi but some remained trapped in their villages where the army has launched "surgical strikes" and mortar shelling in a bid to flush out the militants.
The offensive continued on Friday, prompting Marawi mayor Majul Gandamra to urge the military to avoid using heavy artillery to avoid harming civilians in the area.
