Southeast Asia’s big island nations are to launch a joint naval operation to combat piracy and Islamist militancy that threaten regional trade and security.

Ships and troops from the Philippines, Indonesia and Malaysia plan to deploy next week around seas where hijackings and kidnappings have surged, as fears rise over mounting lawlessness and terrorist threats.

Delfin Lorenzana, Philippine defence secretary, said he hoped the long-mooted campaign around the Sulu and Celebes seas would “keep the sailors safe and also prevent the movement of terrorists from one place to another” in an area with very porous borders.

“We believe now that some of those foreign terrorists . . . came to the Philippines through this back door — and Malaysia and Indonesia are aware of that,” he told the Financial Times. “They are also very concerned about the possible return of other nationals who are now fighting with Isis in Syria.”

… The uptick in piracy follows success by Malaysia and the Philippines in targeting Abu Sayyaf strongholds, according to Collin Koh of Singapore’s S. Rajaratnam School of International Studies. Philippine soldiers killed more than 10 Abu Sayyaf militants in a raid on Sunday in an attempt to free Vietnamese hostages held on a remote southern island, the army said.

“There is a pincer movement which has constrained the group’s activities on land, forcing them to seek revenue on sea,” Mr Koh said.