On Wednesday, General Padilla said that some of those forces, who are usually based in Zamboanga City, had “been moved to help ground forces in Marawi.”
“They are in Marawi, but are not allowed to join combat,” he said.
He declined to say how many American troops were in Marawi, saying only that they were “very few.”
“They are also not engaged in battles, but in case their defenses are breached they are allowed to protect themselves,” he said. The Americans are carrying rifles, he said.
The American presence in Marawi is complicated, and not just because of the possibility that United States troops could get drawn into battle.
The Philippine Constitution prohibits the presence of foreign combat troops, and President Rodrigo Duterte, who has frequently sparred with the United States, a military ally, has threatened to eject American forces from his country.
On Sunday, Mr. Duterte told reporters that he had “never approached America” for help and was unaware of American military assistance in Marawi. His spokesman, Ernesto Abella, said on the same day that the American role “does not involve any boots on the ground.”
Those comments suggested that the Philippine military, which has a long relationship with the American military, may not have consulted Mr. Duterte.
“The only issue here is that when the military operation began in Marawi, the president has instructed the chief of staff and the secretary of national defense to do all they can to defeat this threat,” General Padilla said on Wednesday.
He noted that the United States and the Philippines were bound by a 1951 mutual defense treaty that calls for them to aid each other in times of aggression by a third party.
Hundreds of militants claiming allegiance to the Islamic State attacked Marawi last month with the goal of establishing an Islamic caliphate in the Philippines. The military said 290 people had been killed in the fighting since then, and that the militants still controlled about a fifth of the city.
The United States military said in a statement on Monday that the Special Forces were providing “security assistance and training” in the areas of intelligence, surveillance and reconnaissance.
“For security reasons, we are not able to to discuss specific technical details” of the American support, the statement said.
The Philippine defense secretary, Delfin Lorenzana, told reporters on Sunday that the United States soldiers were gathering information from American P3 Orion spy planes. These planes have been spotted passing over Marawi.
The Americans were “staying inside the camp and coordinating technical communications,” he said, referring to Camp Ranao, which is near Marawi.
Most of the fighting has been confined to one section of the city, but there have been skirmishes and sniper fire in many areas.
Marawi, a once vibrant city of 200,000, has been reduced to a virtual ghost town, with the military continuing to drop bombs in a bid to dislodge the militants. The city is the largest Muslim-majority city in the Philippines, a predominantly Roman Catholic country.
A few hundred civilians are believed to be either trapped in the crossfire or being held hostage by the gunmen, who are led by Isnilon Hapilon, a leader of a faction of Abu Sayyaf, an Islamist insurgency based in the region.
Mr. Hapilon, the leader of the Islamic State in Southeast Asia, is also on the F.B.I. most-wanted-terrorists list, with a $5 million bounty being offered for his capture.
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