Syrian Kurdish fighters, backed by U.S.-led airstrikes, have taken full control of the Syrian border town of Tal Abyad, depriving the Islamic State (ISIS) of a major route used to bring in foreign fighters and supplies.

Tal Abyad is "100 percent under Kurdish control," Redur Khalil, a spokesman for the main Kurdish fighting force, known as the YPG, said by phone from the Syrian-Turkish border on Tuesday. "This is a big blow to the terrorist Islamic State group."

The Syrian Observatory for Human Rights, which monitors the Syria war through activists on the ground, confirmed that the Kurds were in full control of the town.

The capture of Tal Abyad is the Islamic State’s second major military defeat by the Kurds since losing the Kurdish border town of Kobani earlier this year after months of fighting.

Seizing Tal Abyad will enable Kurdish forces to link Kurdish-held areas along the Turkish border, creating a larger unified front against the militants in Syria and paving the way for a more independent Kurdish entity, according to Sami Nader, head of the Beirut-based Levant Institute for Strategic Affairs.

"They’re consolidating the Turkish entity," Nader said.

Khalil said some militants fled from Tal Abyad to Raqqah, ISIS' de facto capital about 50 miles (80 kilometers) to the south, while others slipped into Turkey with people displaced by the fighting. Turkish troops deployed armored cars near the border crossing after suspected Islamic State militants, wearing masks, were spotted on the Syrian side of the border on Sunday, Hurriyet newspaper reported.

ISIS, which set up its caliphate in parts of Syria and Iraq a year ago, still controls the Jarablous crossing on the Syrian-Turkish border, Khalil said.