Syrian rebels operating in southern Damascus have endured serious losses at the hands of the Islamic State group after a surprise offensive launched by the militants in the district of Yalda on Friday, January 13 caught them completely off-guard, Al-Masdar News says.

On Friday, Islamic State-affiliated militants attacked fighters of the Jaysh al-Islam rebel group in the Zein neighborhood of south Damascus’ Yalda district as part of what appears to be a retaliation mission for Jaysh al-Islam’s own attack against ISIS in the same area eight days ago.

The engagement saw IS deploy shock troops, snipers and medium support weapons such as mortars and heavy machine guns. After 12 hours of heavy clashes, IS reportedly captured several rebel positions inside the Zein neighborhood.

Furthermore media linked to IS also claims that rebel forces have suffered casualties of six dead and 30 wounded; at least one prisoner was also taken and later executed.

At present, it is unclear whether or not clashes between IS militants and Syrian rebels in southern Damascus are still ongoing.