TARAKAN, Indonesia (Reuters) - Warships from Indonesia, the Philippines and Malaysia held maneuvers on Monday in waters plagued by insurgency and banditry off north Borneo, launching coordinated patrols in a region where Islamic State influence is growing.

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Helicopters and surveillance planes flew overhead as ministers and army chiefs from the countries attended ceremonies to launch the patrols, with security taking on added urgency after militants overran a town in the southern Philippines.

The Philippine military has said that some of the militants, both domestic insurgents who have pledged allegiance to Islamic State and some foreign fighters, may have mingled with evacuees to slip away during the battle for Marawi City that has raged for almost four weeks.

“We need to watch out for the 500 to 600 terrorists there, 257 of whom have been killed already. The rest, based on information we are getting, are blending in with refugees to get out,” said Indonesian military chief Gatot Nurmantyo.

The spectacular collapse in security in the southern Philippines has alarmed neighbors such as Indonesia and Malaysia.

Indonesia has deployed three Sukhoi fighters to help with security in case militants try to flee southwards towards Indonesia, the head of the Tarakan air base, Colonel Didik Krisyanto, told the state news agency Antara.

Indonesia also inaugurated a maritime command center in the naval base of Tarakan, a town in the province of North Kalimantan on Borneo island, witnessed by the defense ministers and army chiefs from the three countries.

Malaysian defense minister Hishammuddin Hussein said the three countries would increase the sharing of information because what had happened in Marawi could happen elsewhere.

The neighbors would not allow Islamic State “to set foot, even just an inch, in our region”, he said.

Maritime command centers will also be set up in Tawau in Malaysia’s Sabah state, also on Borneo, and Bongao in the Philippines.

“We see these functioning as a triangle, like a spider’s web, where everything inside the triangle will be monitored,” said Nurmantyo said of the centers.

A port town, Tarakan is just south of the Malaysian side of Borneo and looks out across to Mindanao in the southern Philippines, a sprawling island that has suffered from hostage taking and piracy for decades.

Indonesian naval authorities had asked residents including fishermen in border areas facing the Philippines to report any suspicious people, Antara reported.

Illustrating the insecurity in the area, Eman, a 31-year-old fisherman from a village near Tarakan, said he was robbed three times last year by pirates in speed boats.

“They fired warning shots one time and forced us to lie face down,” he said.