It was not immediately clear whether civilians were among the dead.
In his speech to the troops, Duterte said said ISIS "is here already" and flying its flags.
Snipers fired on Friday afternoon at about 100 troops who were marching single-file uphill through one district of Marawi that the militants had previously controlled, according to journalists accompanying the soldiers.
Galvez said the military managed to gain control of "some areas" but admitted that there are still areas which are still under the control of the Maute militants. "If you can not be convinced to stop fighting, so be it", Duterte said. The military said he is still wounded from a January air strike and being protected by his fighters.
An OV-10 bomber flies to drop bombs during a continuous assault with insurgents from the so-called Maute group in Marawi City.More news: North Korea's Kim rejects olive branch from Trump
Iligan City is roughly one hour from Marawi, where Maute and Abu Sayyaf militants have been fighting government forces since Tuesday.
Bomb drops may be expected to continue as the military is eyeing "more surgical airstrikes" to quickly clear the city of the local terrorist groups.
"We take a serious view of anyone who supports, promotes, undertakes or makes preparations to undertake armed violence regardless of where the violence takes place". "We have to finish this".
"In as much as we would like to avoid collateral damage, these rebels are forcing the hand of government by hiding and holding out inside private homes, government buildings and other facilities", military spokesman Brigadier-General Restituto Padilla said. "May the loving God protect the people of Marawi", said the cardinal, whose see is also on Mindanao. "We suspect that, but we're still validating", he said.
Police Chief Romeo Enriquez said there may have been confusion because his predecessor in Malabang, a town near Marawi, was killed in the fighting on Tuesday, although he was not beheaded. Mr Enriquez has been in the job for about two months.More news: Texas lawmakers pass controversial bathroom, adoption bills
Duterte's use of martial law has raised concerns among human rights groups, who have accused him of ordering security forces to kill thousands of people as part of his crackdown on illicit drugs.
Teachers who were trapped in the siege by Muslim militants of Marawi city wait for their transport back to their hometowns in southern Philippines Thursday, May 25, 2017.
It has transmogrified into invasion by foreign terrorists who heeded the clarion call of the ISIS to go to the Philippines if they find difficulty in going to Iraq or Syria. The Philippine army has been trying to flush out rebels of the Islamic State-linked Maute group from the island. Hapilon is on Washington's list of most-wanted terrorists and has a $5 million bounty on his head.
The southern Philippines, particularly the resource-rich but poverty-wracked Mindanao region, has always been a hotbed of activity by the Abu Sayyaf and other fundamentalist groups. But recent attacks and this week's siege suggest the threat of extremist ideology may be growing. "Martial law and the heightened vulnerability to military abuse that it brings to women and children are not a joke either." r Duterte's aides frequently explain away his most controversial comments as being "merely rhetoric" or comments which only ordinary Filipinos would appreciate.
Gunaratna said Duterte's concern about the growth of ISIS in the southern Philippines was warranted, but that martial law was unlikely to solve the problem. Martial law was last declared nationwide in 1972, when then-dictator Ferdinand Marcos used it to preserve his grasp on power for over a decade.More news: Woah! Kourtney's Ex Scott Gets Hot and Heavy with Bella Thorne