DAMASCUS - After suffering losses to the Kurdish fighters in northern Syria, the Islamic State (IS) militants unleashed a retaliatory offensive against predominantly Kurdish areas in northern Syria on Thursday.

The terror-labeled group started simultaneous attacks against the Kurdish fighters in the predominantly-Kurdish city of Ayn al-Arab, or Kobane, and against the Syrian government forces in the city of Hasaka in northern Syria.

In Ayn al-Arab, in the northern countryside of Aleppo province near Turkey, the IS militants infiltrated the city in disguise, wearing the uniform of the Kurdish fighters of the People's Protection Units (YPG) and allied rebel groups, said the Syrian Observatory for Human Rights, a UK-based watchdog group.

The IS members infiltrated parts of the city and snipers fanned out in several areas, triggering violent battles with YPG fighters,

during which 22 IS militants and 35 people, including YPG fighters, were killed.