IS fighters have been taking advantage of sandstorms to stage attacks, according to the Syrian Observatory for Human Rights
The Islamic State (IS) group killed 68 US-backed fighters near Syria's Hajin, an eastern IS holdout on the Iraqi border, an activist group said on Saturday.
IS late on Friday used suicide bombers as part of a counter-attack against the Syrian Democratic Forces (SDF), who have been fighting the group with US backing, the UK-based Syrian Observatory for Human rights said.
According to the Observatory, IS has been taking advantage of recurring sandstorms in the eastern countryside of the Deir Ezzor province in recent weeks to carry out deadly strikes against the SDF.
The attack came a day before a summit in Istanbul, where the leaders of Russia, France, Germany and Turkey are aiming to find a lasting political solution to the Syrian civil war and salvage a fragile ceasefire in Idlib, a rebel-held northwestern province.
A week earlier, offensives by US-backed forces killed 35 IS fighters near Hajin.
IS overran large areas of Syria and neighbouring Iraq in 2014, proclaiming a "caliphate" across the land it controlled.
But the group has since lost most of its territory to various offensives in both countries.
In Syria, its presence has been reduced to parts of the vast Badia desert and the Hajin pocket near the Iraqi border.
Syria's war has killed more than 360,000 people since it erupted in 2011 with the brutal repression of anti-government protests.