Foreign fighters are among Islamist militants killed in a southern Philippine city over the past days, officials say.
Six jihadists, including Indonesian and Malaysian citizens, were killed as the army continued its operation to drive the rebels out of the city of Marawi.
Attack helicopters and special forces have been deployed in the offensive.
It is a rare admission by the authorities that local jihadists are working with international groups.
Marawi is a mainly Muslim city in Lanao del Sur province on the southern island of Mindanao. The province is a stronghold for the Maute group, which has pledged allegiance to so-called Islamic State (IS).
What is happening in Marawi?
Fighting erupted after a failed army raid to capture a top militant leader. At least 11 soldiers and 31 militants have been killed, a military spokesman said.
Philippine President Rodrigo Duterte imposed martial law in Mindanao on Tuesday in response to the violence.
Martial law allows the use of the military to enforce order and the detention of people without charge for long periods.
What’s the IS link?
Manila’s solicitor-general said that what used to be domestic rebels have now subscribed to the ideology of IS.
“What is happening in Mindanao is no longer a rebellion of Filipino citizens. It has transmogrified into an invasion by foreign fighters,” Jose Calida told a news conference.
“They want to make Mindanao part of the caliphate.”
The government had always downplayed the numbers of foreigners amongst the local fighters, Sidney Jones, director of the Institute for Policy Analysis of Conflict in Jakarta told the BBC.
“And it’s crucial that the government acknowledges that there is a serious IS problem in the Philippines,” she says, explaining that a much better co-ordination between local and national authorities was needed to deal with the situation.
The admission confirms what observers see as moves by IS targeting the majority Muslim southern Philippines to establish a stronghold in South East Asia.
“It is clear that the number of men from both Indonesia and Malaysia who have travelled to Mindanao has increased over the past year,” Ms Jones explains.