The terrorist threat facing Southeast Asia is growing as foreign fighters return to the region, Southeast Asian defence ministers said in a joint statement on Tuesday in which they pledged to improve cooperation to tackle militancy.

Six Southeast Asian nations launched an intelligence pact last month aimed at combating Islamist militants and improving cooperation on security threats, overcoming what analysts described as a high level of distrust. They also pledged to increase cooperation in July.

“We, the Defence Ministers of the Association of Southeast Asian Nations [ASEAN], note with grave concern the rise of terrorism in our region, perpetrated by individuals and groups with increasingly sophisticated and deadly tactics and weapons,” they said at the conclusion of their two-day meeting in Singapore.

“The scale and complexity of the terrorist threat faced by our region continues to grow with the influx of returning foreign terrorist fighters and cross border movement of terrorists.”

The ministers said they would also improve cooperation with external partners.

The push for further regional cooperation comes after insurgents aligned to Islamic State laid siege to the southern Philippine city of Marawi last year.

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That battle sparked alarm that as Islamic State suffered reversals in Iraq and Syria, it was seeking to create a stronghold in Southeast Asia, buttressed by fighters returning from the Middle East.

ASEAN consists of Indonesia, which has the world’s biggest Muslim population, and mostly Muslim Malaysia alongside Brunei, Cambodia, Laos, Burma, the Philippines, Singapore, Thailand and Vietnam.

Singapore, ranked one of the safest countries in the world, has also been stepping up efforts to deter terrorism in recent years.