Philippine forces controlled most Marawi where gunmen linked to the Islamic State group launched a bloody siege nearly a week ago, authorities said Monday, as they put a neighbouring city on lockdown over fears of infiltration by militants.

The city of Iligan, about 38 km away, was overflowing with evacuees who were subject to stringent security checks over fears Islamist militants had sneaked out of Marawi, one of the biggest Muslim cities in the mainly Catholic Philippines.

The clashes in Marawi with the Maute militia, a group hardly known a year ago, has become the biggest security challenge of Rodrigo Duterte’s 11-month presidency, with gunmen resisting air and ground assaults and still in control of central parts of a city of 200,000 people.

The military said the rebels may be getting help from “sympathetic elements” and fighters they had freed from jail during the rampage that started on Tuesday and caught the military by surprise.

“Our ground commanders have assured that the end is almost there,” military spokesman, Restituto Padilla said.

More than 100 people have been killed, most of them militants, according to the military, and most of the city’s residents have fled.

The military said the Maute group

Some troops tried to eliminate Maute snipers on Monday as others guarded deserted streets, taken back block-by-block.

Helicopters circled the lakeside city and smoke poured out of some buildings. Artillery explosions echoed.

Though most people have left, thousands are stranded, worried they could be intercepted by militants at checkpoints on routes out of the city.

There were still bodies of civilians in Marawi and residents urged the military to halt air strikes, said Zia Alonto Adiong, a politician involved in evacuation efforts.

was still present in nine of the city’s 96 Barangays, or communities.

The Maute group’s ability to fight off the military for so long will add to fears that Islamic State’s radical ideology is spreading in the southern Philippines and it could become a haven for militants from Indonesia, Malaysia and beyond.

A Reuters photographer saw an Islamic State flag in an oil drum in an abandoned street on Monday, where chickens roamed in front of damaged shops and homes.

Colonel Alex Aduca, chief of the Fourth Mechanised Infantry Battalion said the military was “intensifying the security operations” to prevent the militants from sneaking into Iligan city.

“We don’t want what’s happening in Marawi to spill over in Iligan,” said Aduca said.

Sixty-one militants, 20 members of the security forces and 19 civilians have been killed since Tuesday, when Maute rebels went on the rampage after a botched military operation to arrest Isnilon Hapilon, who the government believes is a point man for Islamic State in the Philippines.