A view of the Maute group stronghold with an ISIS flag in Marawi City in southern Philippines, May 29, 2017. Reuters

Militants affiliated with the Islamic State (IS) group have been locked in street-to-street battles with the government security forces in Marawi, a southern Philippine city, where 19 civilians were killed, the military said Sunday. This brought the official death toll from nearly a week of fighting to at least 85, reports said.

61 militants, 20 members of the security forces and 19 civilians have been killed in past one week when Maute rebels went on a rampage in Marawi. The rebels did so after a failed attempt by the military to arrest Isnilon Hapilon, who is believed to be a pivotal man for ISIS in the Philippines, reports said.

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Terrorism analysts had warned months ago that ISIS could surge in Southeast Asia as the terror group lost its territory in the Middle East.

“ISIS has publicly accepted pledges from various groups in the Philippines and has called on followers in Southeast Asia to go to the Philippines if they cannot travel to Syria,” an American intelligence official who spoke with the Washington Times on the condition of anonymity said.

The group “harbors global ambitions and seeks to expand its influence in Southeast Asia by cultivating a network of adherents and supporters,” the official said adding “As it has done in its main battle space of Iraq and Syria, ISIS seeks to exploit ungoverned space.”

Philippine President Rodrigo Duterte, who is facing the biggest security challenges, responded to the violent situation by declaring martial law across the southern tier of the Philippines. He even warned that he could expand it to the entire island nation of 100 million, CNN reported.

Iligan, 24 miles away from Marawi, was overflowing with evacuees Monday who have fled Marawi over fears of being attacked by Islamist militants. Almost 200,000 people have left Marawi, and some of them have found shelter in Iligan. However, authorities fear Maute fighters were disguising themselves as displaced people to get access to Iligan where they could possibly launch attacks, Reuters reported.

"We don't want what's happening in Marawi to spill over in Iligan," Colonel Alex Aduca, chief of the Fourth Mechanized Infantry Battalion said.

"We want to ensure the safety of people here, to prevent elements from entering and conducting terroristic activities," he told DZMM radio. He also said some rebels had been caught trying to enter Iligan. However, he did not reveal further details.

The military announced Saturday it would intensify the bombing campaign, reports said. Saturday also marked the beginning of the holy month of Ramadan.

“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.

“Their refusal to surrender is holding the city captive. Hence, it is now increasingly becoming necessary to use more surgical airstrikes to clear the city and to bring this rebellion to a quicker end," Padilla added.

"Black ISIS flags with the words "There is no god but God" were seen in Marawi," Chico Usman, a resident of Saguiaran, a town outside Marawi, told CNN.

While Islamist and criminal groups have been active in the lawless tri-border area between the Philippines, Malaysia, and Indonesia for years, aggressive attacks like the ones that are happening since the past week on government troops by militants loyal to ISIS, have increased fears over the group's expansion into Southeast Asia, reports said.