American forces have transferred their operations from Zamboanga City to war-torn Marawi City where the Armed Forces of the Philippines has been pursuing the Islamic State-linked Maute Group, a military spokesman said on Wednesday.

In the "Mindanao Hour" briefing in Malacanang, Brig. Gen. Resituto Padilla said the "small number" of US forces moved to Marawi.

"Now that there are skirmishes in Marawi, their capacity has been transferred in order for them to help the ground commanders in Marawi," Padilla said.

"I'm not sure of the exact number, but very small. Those who are helping in operating and maintaining the equipment," Padilla said when asked how many American soldiers have been extending "technical assistance" in Marawi.

He said the US forces have been in the country, particularly stationed in Zamboanga, for quite a time since they have been helping the government in pursuing the Abu Sayyaf Group in Sulu, Basilan, Tawi-Tawi and nearby areas.

It was the Philippine government who sought the assistance of the American forces, Padilla said, adding the foreign troopers' presence in the country is under the 1951 Mutual Defense Treaty of the two countries.

Padilla also justified why the American forces have to carry firearms with them even if they were not involved in combat operations.

He said the foreign troops have "to protect themselves" because there could be a possible breach of defenses.

President Rodrigo Duterte earlier admitted that he was not aware that American forces have been helping the Filipino soldiers in fighting the Maute militants.

But he has thanked US for its assistance. Celerina Monte/DMS