A leading Filipino authority has claimed there are foreigners in amongst the islamists on Mindanao island.
The attorney general of Manila, Jose Calida, made the claim as government forces continue to battle against fighters linked to Islamic State.
Calida claimed there were Malaysians and Indonesians battling government forces alongside the Islamists.
The president of the Philippines, Rodrigo Duterte, has imposed martial law on the island, and there have been fierce struggles against Islamist combatants as the government tries to take back control.
A major offensive was launched this week in Marawi City, which has resulted in churchgoers being taken hostage and a local police chief being beheaded, among other clashes.
The president has made it clear martial law could remain in place for a year, if necessary.