For nearly a month now, terrorists brandishing the black flag of the Islamic State in Iraq and Syria (ISIS) have held back - with anti-tank weapons, machine guns, sniper rifles and Molotov cocktails - an entire army brigade trying to retake the southern Philippine city of Marawi.
As of yesterday, the militants remain in control of at least four districts, a river separating them from Marawi's seat of government.
This pitched battle, which began when the Abu Sayyaf and Maute groups stormed Marawi on May 23 in an audacious bid to turn it into an ISIS "province", is unlikely to end soon. This has many in the region worried.
Analysts warn that the longer the fighting in Marawi drags on, the more it will inspire disparate groups of militants to coalesce into a new organisation with a common command structure under ISIS' sway.
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Islamist militants are also seeing in the long-drawn conflict in Marawi that it is possible, with just a handful of men, to hold a territory in the Philippines' war-torn southern island group of Mindanao.
The well is deep. Nearly all provinces in Indonesia reportedly have "sleeper cells". A Washington-based think-tank is keeping tabs on at least 20 ISIS-linked groups, including Jemaah Islamiah splinters. Even Thailand, with a festering insurgency in its mainly Malay-Muslim south, is susceptible to ISIS infiltration.
A problem this big and insidious will require a wider, more coordinated and more targeted response. The Philippines, Indonesia and Malaysia are heading in the right direction as they begin joint patrols of terrorist-plagued waters off the Sulu archipelago, Sabah state and Indonesia's northern Kalimantan and Sulawesi territories this week. But so much more has to be done because Marawi has changed the game.