"As a result of the fierce clashes, 14 of our fighters rose to the rank of martyrdom, while others were wounded," stated SDF spokesperson Kino Gabriel late on Saturday.
The UK-based Syrian Observatory for Human Rights has monitored the conflict for years. It reported ISIS had killed 68 members of the Kurdish-led SDF on Friday night.
"ISIS terrorists continue to launch counter-attacks, taking advantage of adverse weather conditions and lack of vision due to sandstorms in the region, which was carried out by the ISIS on the morning of Friday..." added Gabriel.
He described ISIS's losses as "heavy" in lives and equipment and said the US-led international coaliton was continuing support without specifying the type of support.
The region has experienced repeated dust storms.
Coalition forces had reportedly suspended air support missions in the area.
When approached by Rudaw, the US-led coalition declined to comment on the incident or the alleged suspension of air support.
According to the Observatory, ISIS captured 10 SDF fighters, seized two American Hummer vehicles, and radio communications equipment on Wednesday.
A Kurdish commander said last week that the fight against ISIS is taking “longer than expected,” because of weather conditions and the concentration of hardcore jihadists with years of fighting experience.
Operation Roundup began on May 1 with the coalition and SDF. Its third phase aims to clear ISIS from east of the Euphrates near Al Boukamal along the border with Iraq.
US President Donald Trump has bragged of his administration's success against ISIS, while the military and diplomats have been more cautious in their wording.
"Our work is not over," said US Special Presidential Envoy to the Global Coalition to Defeat ISIS at the IISS Manama Dialogue in Bahrain on Saturday.
