A military spokesman, Brigadier General Restituto Padilla, said Monday that only small areas of Marawi were still controlled by gunmen from a local rebel group with ties to "Islamic State" (IS).

"We can control who comes in and who comes out, who moves around and who doesn't, and we are trying to isolate these pockets of resistance that have remained," Padilla said.

Militants from the pro-IS Maute rebel group have been holed up inside buildings for a week, fending off helicopter airstrikes, armored vehicles and ground attacks by government troops. The military said the group was still present in nine of Marawi's 96 districts.

About 100 people have died in the violence, including more than 20 civilians. On Sunday, Philippine forces said they found corpses in the streets, including at least eight men who appeared to have been executed.

Government troops backed by helicopters and armored cars are trying to drive Islamist militants out of Marawi

Evacuees pour into Iligan

Many of Marawi's 200,000 inhabitants have fled to the nearby city of Iligan, while more than 3,000 others remain trapped in the city's conflict zones, according to the Red Cross.

"They are texting us and calling us for help," Zia Alonto Adiong, spokesman for the provincial crisis management committee, said. "They can't leave because they are afraid of running into checkpoints put up by the gunmen."

Authorities said there was also a risk militants were escaping by passing themselves off as displaced civilians in order to launch attacks in Iligan.

"We are trying our best to ensure that the terrorist activities will not spill over," Colonel Alex Aduca, an infantry battalion commander, told the German Press Agency. "We are intensifying our security operations… We have provided containment areas so that we can process evacuees properly."

Martial law

President Rodrigo Duterte declared martial law in the southern Mindanao province last week after Maute rebels went on a rampage through Marawi. Some rights activists and lawmakers warned that imposing the measure across the whole region, where both Marawi and Iligan are located, could increase the risk of human rights abuses by security forces.

The militants began their siege on Tuesday after a botched government attempt to capture Isnilon Hapilon, a former leader of the notorious Abu Sayyaf gang and the Philippine head of IS. Hapilon is also thought to lead an alliance of several smaller militant groups, including the Maute, which has a heavy presence in Muslim-majority Marawi.

The group has around 260 armed followers, according to government estimates. Fighters from Malaysia, Indonesia and Singapore are also believed to have joined its ranks.

Muslim separatists have waged an insurgency in Mindanao for decades, and the latest crisis has raised fears that extremism is growing in the southern region.

Watch video 00:30 Hundreds flee fighting in southern Philippines

nm/msh (AP, AFP, Reuters, dpa)