TARAKAN, Indonesia - Warships from Indonesia, the Philippines and Malaysia held maneuvers on Monday near a naval base in northern Borneo to mark the launch of coordinated patrols to beef up security in waters plagued by insurgencies and banditry.

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

The Philippine military has said that some of the Islamist militants, who were made up of local insurgent groups that have pledged allegiance to Islamic State but also 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.

Worsening 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 at the weekend.

• READ: Indonesia deploys Sukhoi jets to guard against fleeing militants -state media

Indonesia on Monday 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 defence ministers and army chiefs from the three countries.

Maritime command centers to coordinate the patrols and information sharing will also be set up in Tawau in Malaysia's Sabah and Bongao in the Philippines.

"We see these (command centers) functioning as a triangle, like a spider's web, where everything inside the triangle will be monitored," said military chief Nurmantyo.

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.

"Maintaining marine security is the duty of ASEAN countries and not other countries," said Indonesian defense minister Ryamizard Ryacudu, referring to the Association of South East Asian Nations (ASEAN).

Singapore and Brunei also attended the launch of patrols as observers.

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

A police mobile brigade corp had also been sent to northern areas on Sulawesi island to prevent militants from crossing the border, it said. (Writing by Ed Davies; Editing by Michael Perry)