DAMASCUS - The Syrian Democratic Force (SDF), a new Western-backed rebel alliance, continued its progress against the Islamic State (IS) group in Syria's al-Hasakah province near the Iraqi borders on Sunday, a monitor group reported.

The SDF captured the Mailabiyeh military base, which was taken by IS in July 2014 following battles with the Syrian army, according to the Syrian Observatory for Human Rights.

The Observatory said the US-led anti-terror coalition backed the SDF in their push to take the base, adding that tens of the IS militants were killed during the battles.

The fresh achievement came just a week after the SDF captured the key town of Hawl in the southern countryside of al-Hasakah.

The SDF, an alliance of Kurdish, Syrian Arab, Assyrian Syriac Christian and Turkmen militias in cooperation with the Kurdish People's Protection Units (YPG), said their aim is to fight the IS in northern Syria.

Earlier this month, the YPG spokesman Salah Jamil told Xinhua that the SDF managed to free large areas in the southern countryside of al-Hasakah from the IS control.

The control of al-Hasakah is split between the YPG and the Syrian government forces.

The Kurds are in control of the majority of northern al-Hasakah and the borderline with Turkey, while the IS terror group control the city of Shadadi and its villages south of al-Hasakah and areas in the eastern and western countryside of that province.