Troops aboard helicopters and in armoured tanks battled Daesh-linked militants inside a southern Philippine city on Thursday, as reports emerged of the gunmen murdering civilians.
The army sent about 100 soldiers, including US-trained special forces, to retake buildings and streets in Marawi City held by militants of the Maute group, which pledged allegiance to Daesh. At least 21 people have been killed since Duterte imposed martial law late on Tuesday on impoverished Mindanao, the country's second-largest island, to prevent the spread of extremism after the rebels rampaged through Marawi.
Hundreds of civilians, including children, are taking shelter in a military camp in the city. The militants have been holding several Christians hostage and set free more than 100 prisoners from two jails.
Religious leaders have also accused the rebels of using the Christian hostages as human shields.
Marawi mayor Majul Gandamra said some rebels from the Maute were still holed up in buildings and sporadic gunfire could be heard.
He said troops had isolated the guerrillas but were not engaging them. The rebels were posting images on social media to make known their sustained presence in Marawi, Gandamra said.
Marawi has about 200,000 residents but many of them have fled because of the fighting.
Authorities have not reported any civilian casualties but the GMA television network showed images of nine people who had apparently been shot dead. The victims had their hands tied together.
They were captured at a roadside checkpoint and murdered by the militants after being identified as Christians, according to the GMA reporter who cited a witness.
A hornet's nest
The fighting erupted on Tuesday after security forces raided a house where they believed Isnilon Hapilon, a leader of the infamous Abu Sayyaf kidnap-for-ransom gang and Philippine head of Daesh, was hiding.
The United States regards Hapilon as one of the world's most dangerous terrorists, offering a bounty of $5 million for his capture.
However, the raid went spectacularly wrong as dozens of gunmen emerged to repel the security forces, then went on a rampage across the city while flying black Daesh flags.
The militants raided two jails, leading to the escape of more than 100 inmates, according to Mujiv Hataman, the governor of a Muslim self-rule area that includes Marawi.
They also set fire to many buildings, including a church and a university.