Kurdish fighters backed by intense U.S.-led airstrikes pushed the Islamic State group entirely out of a key Syrian town on Monday, marking a major defeat for the extremists whose hopes for an easy victory when they pushed into Kobani last year dissolved into a bloody, costly and months-long siege.

As their victory neared, the Kurdish troops earlier in the day raised their flag on a hill overlooking the town just across the border with Turkey, replacing the Islamic State group's black banner.

The battlefield success is a major conquest both for Syria's embattled Kurds and the U.S.-led coalition, whose American coordinator had predicted that the Islamic State group would "impale itself" on Kobani.

The Britain-based Syrian Observatory for Human Rights and Kobani-based Syrian activist Farhad Shami said the Islamic State, also known as ISIS or ISIL, had been fully expelled, with some sporadic fighting on the ouster eastern edges of the town.

In September, Islamic State fighters began capturing some 300 Kurdish villages near Kobani and thrust into the town itself, occupying nearly half of it. Tens of thousands of refugees spilled across the border into Turkey.

By October, the IS group's control of Kobani was so widespread that it even made a propaganda video from the town featuring a captive British photojournalist, John Cantlie, to convey its message that Islamic State fighters had pushed deep inside despite U.S.-led airstrikes.

Kobani, whose capture would have given the jihadi group control of a border crossing with Turkey and opened direct lines between its positions along the border, quickly became a centerpiece of the U.S.-led air campaign in Syria. U.S. Secretary of State John Kerry declared it would be "morally very difficult" not to help Kobani.

The U.S.-led air assault began Sept. 23, with Kobani the target of about a half-dozen airstrikes on average each day, and often more. More than 80 percent of all coalition airstrikes in Syria have been in or around the town. At one point in October, the U.S. air campaign dropped bundles of weapons and medical supplies for Kurdish fighters -- a first in the Syrian conflict.

Analysts, as well as Syrian and Kurdish activists, credit the campaign and the arrival in October of heavily armed Kurdish peshmerga fighters from Iraq, who neutralized the Islamic State group's artillery advantage, for bringing key areas of the town under Kurdish control.

Idriss Nassan, a senior Kurdish official, said U.S.-led coalition strikes became more intense in the past few days, helping Kurdish fighters in their final push toward Islamic State group positions on the southern and eastern edges of the town.

The U.S. Central Command said Monday that it had carried out 17 airstrikes near Kobani over the last 24 hours that struck Islamic State group infrastructure and fighting positions.

Nassan said he was preparing to head into Kobani on Tuesday and expected the town to be fully free by then.