The United States said it had been providing the Armed Forces of the Philippines (AFP) with technical assistance to end the siege.
Thirteen Philippine marines were killed in fierce fighting with militants who have laid siege to southern Marawi city for almost a month in the biggest single-day loss for government forces, the military said on Saturday.
A United States official, who requested anonymity, confirmed to Philippine media that the support they are providing to soldiers to suppress terrorism is in form of aerial surveillance and they are providing electronic eavesdropping and communications assistance.
The seizure of Marawi by hundreds of fighters who have sworn allegiance to the IS, including dozens from neighboring countries and the Middle East, has fueled concern that the ultraradical group is gaining a foothold in Southeast Asia. In response, Duterte had vowed to expel USA military personnel from the country, but the leader appears to have found a more sympathetic counterpart in President Donald Trump, who has reportedly praised Duterte's brutal anti-crime program.
The Filipino president did not comment on allegations that Philippines military officials bypassed his authority to request assistance from US Special Forces, instead remarking that, "our soldiers are pro-American, that I can not deny".
The marines were on an operation to rescue about 100 hostages held by the militants, who set off improvised explosive devices and fired rocket-propelled grenades at the advancing troops, Herrera said.
So far, 58 members of the Philippines security forces, 158 Maute fighters and 21 civilians have been killed in the fighting.
Filipinos marked their country's Independence Day by raising the national flag Monday in a southern city where troops pressed assaults to quell a three-week siege by Islamic State group-aligned militants that has left 270 combatants and civilians dead.
A US P3 Orion surveillance aircraft flying over the town of Marawi city.
Forty soldiers were also wounded in the 14-hour firefight on Friday in Marawi City, 800 kilometres south of Manila, said marine spokesman Colonel Edgard Arevalo.
KMP also expressed grief over the displacement of more than 200,000 residents of Marawi due to the continuing war. "I never approached any American to say that "please help us", he said.
Philippines laws provide that the President of the Republic will serve as the Commander-in-Chief of the Armed Forces of the country and as commander-in-chief.
According to GMA News, there have also been reports of the extremists using child soldiers to fight for them with children as young as 10 seen carrying M-16 rifles.
But even after the US said it was providing assistance at the request of the government, President Duterte was quick to deny he sought any support from Washington.