DAMASCUS, Jan. 8 (Xinhua) -- At least 55 fighters of the Kurdish-led Syrian Democratic Forces (SDF) were either killed or wounded in a counterattack unleashed by the Islamic State (IS) in eastern Syria, a war monitor reported on Tuesday.

The IS militants launched their counter-offensive on the town of Shoufeh, which they had lost to the SDF over the past 24 hours, in the eastern bank of the Euphrates River in eastern Deir al-Zour province.

The militants took advantage of a sandstorm that hit the area when launching their attack on the SDF, according to the Syrian Observatory for Human Rights.

The Observatory said intense battles are taking place between the SDF and IS in that area.

The SDF fighters have recently succeeded with the help of the U.S.-led coalition to besiege the IS militants in two towns in the eastern Euphrates region after launching their campaign in that area in September of last year.