TARAKAN, Indonesia — Southeast Asian neighbors Indonesia, Malaysia and the Philippines launched coordinated maritime patrols on Monday to intensify their fight against Islamic militants who have laid siege to a southern Philippine city.

Defense ministers and military chiefs from the three countries launched the patrols in the Indonesian city of Tarakan in northern Borneo, just across the border from Sabah, Malaysia.

Indonesia's military chief, Gen. Gatot Nurmantyo, said maritime command centers were also opened in the cities of Tawau in Malaysia and Bongao in the Philippines. The information and intelligence sharing centers establish designated sea lanes for ships in the seas along the countries' borders to prevent Islamic State group-aligned militants in the southern Philippines from fleeing to neighboring nations.

The conflict in the Philippine city of Marawi has raised fears that ISIS' violent ideology is gaining a foothold in the country's restive south, where Muslim separatists have fought for greater autonomy for decades.

Nurmantyo said the idea of the trilateral maritime patrols was initiated by the countries last year to maintain stability in the region in the face of threats such as piracy, kidnapping, terrorism and other crimes in regional waters.

"This trilateral cooperation is needed to anticipate infiltration possibility of IS-aligned militants from Marawi disguised as refugees," Nurmantyo said in a speech, using an alternative acronym for the Islamic State group.

Philippine military spokesman Brig. Gen. Restituto Padilla said the coordinated patrols aim to tighten protection along porous borders and prevent abductions at high seas. They will also help prevent the movement of fugitives seeking haven in a different country or planning to provide assistance to jihadists, he said.

He said immigration procedures should also be strengthened since they are the first line of defense in blocking militants who come in through the countries' airports.

"The enemy we face right now is a different breed, and with the presence of foreign fighters in the area — a matter that we are trying to validate and prove based on whatever we recover from the field — is part of that continuing concern," he told reporters in the Philippines.  He was referring to the reported presence in Marawi of foreign fighters, who he said bring a kind of terrorism seen in the Middle East but not practiced by local militants.

Thousands of troops and police are struggling to end the 28-day siege by Muslim militants aligned with ISIS. Officials said the fighting has left at least 26 civilians, 257 militants and 62 security forces dead.

Monday's opening ceremony of the joint patrols was held on board an Indonesian warship and was attended by security officials from Singapore and Brunei, who acted as observers.

Authorities in Indonesia, the world's most populous Muslim-majority nation, have carried out a sustained crackdown on militants since bombings on Bali in 2002 by al-Qaida-affiliated radicals that killed 202 people. In recent years, it has faced a new threat as the rise of ISIS in the Middle East has breathed new life into local militant networks and raised concerns about the risk of Indonesian fighters returning home from fighting with ISIS.

Marawi is 750 kilometers northeast of Tarakan in Indonesia's North Kalimantan province.

Associated Press writer Teresa Cerojano in Manila, Philippines, contributed to this report.

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