LAST ISIL OUTPOST IN SYRIA UNDER U.S.-BACKED ATTACK.

The last vestige of Islamic State territory in Syria came under attack, as members of a U.S.-backed coalition said Tuesday that they had begun a final push to oust the militants from Hajin, the remaining sliver of territory under the group’s control in the region where it was born.

The assault is the final chapter of a war that began more than four years ago after the Islamic State group seized enormous tracts of land in Iraq and Syria and declared a caliphate.

The Syrian Democratic Forces, the Kurdish-led militia that has been fighting the Islamic State in Syria with the United States and its allies, said in a statement that its forces had launched an offensive on the area from four sides Monday evening.

Even if it is defeated in Hajin, however, the Islamic State is likely to remain a powerful terrorist force.

The Syrian Democratic Forces is preparing for a slog: between two and three months, according to one senior official with the militia.

“We expect a long and hard fight,” said Col. Sean Ryan, a spokesman for the U.S.-led military coalition in Baghdad. “These are the diehard fighters with nowhere else to go.”

In its remaining slip of land, the Islamic State has dug tunnels. Its fighters, aerial surveillance indicates, have mined the circumference of their last redoubt, laying explosive devices on the roads leading into the area.

And to facilitate escape, they have buried large quantities of cash in berms of sand and hidden weapons and ammunition in caves and underground passages, strategically positioning resources in the desert, analysts say.

Driving the militants from their territory alone will not be enough to bring about their long-term defeat, officials and analysts say. The Islamic State remains capable of wreaking damage around the world simply by inspiring adherents to take up a gun, a bomb or even a car. And in Iraq and Syria, the group has reverted to an insurgency.

Meanwhile, UN SecretaryGeneral Antonio Guterres is appealing to all parties directly and indirectly involved in Syria — especially Iran, Russia, and Turkey — to protect civilians and avoid a “bloodbath” in the last major rebel-held stronghold in Idlib.

He said a full-scale battle in Idlib “would unleash a humanitarian nightmare unlike any seen in the bloodsoaked Syrian conflict.”

Guterres said he understands that “the present situation in Idlib is not sustainable and the presence of terrorist groups cannot be tolerated.”

But the UN chief said it is especially important that Iran, Russia and Syria “find a way in which it is possible to isolate terrorist groups and ... create a situation in which civilians will not be the price paid to solve the problem in Idlib.”