SDF launched their offensive to retake Hajin on Sept. 10. It has been a grueling campaign, with sand storms and fog at times grounding coalition aircraft, allowing the militants to launch counteroffensives that have killed hundreds of SDF fighters. IS has also taken scores of prisoners and hundreds of civilians hostage.

"It is very difficult because we are in the last stages, where almost every ISIS fighter is a suicide belt," Brett McGurk, the White House envoy for the war against IS, said at a security conference held recently in the Gulf nation of Bahrain.

The extremists, besieged near the border, have no place to go. They are surrounded from the east and north by SDF fighters while from the south and west, Syrian government forces and their allies haveclosed roads to the surrounding desert.

The Britain-based Syrian Observatory for Human Rights says since the fighting began nearly three months ago, 1,616 people have been killed, mostly fighters from both sides. It said the dead include 827 IS gunmen, 481 SDF fighters and 308 civilians.

The fighting is now believed to be in its final stages, with SDF fighters said to have broken IS defenses and taken the fight inside the town.

The fall of Hajin will end the group's hold over any significant territory in Iraq or Syria, but sleeper cells in both countries will continue to stage attacks amid attempts to regroup. IS affiliates in Libya, Afghanistan and Egypt's Sinai Peninsula continue to stage regular attacks.

The group's savage legacy, meanwhile, will stay on for years to come.

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