Clashes between Russia-backed Syrian regime forces and the Islamic State group have killed more than 50 fighters on both sides in two days, a Britain-based war monitor said on Saturday. Fighting and Russian air strikes in the central desert province of Homs since late Thursday have claimed the lives of 20 pro-government fighters and 31 jihadists, the Syrian Observatory for Human Rights said. IS jihadists have retained a roving presence in Syria's vast Badia desert, despite losing their last shred of territory last year. They regularly carry out attacks there. IS declared a cross-border "caliphate" in large parts of Syria and neighbouring Iraq in 2014, but several military campaigns against it chipped away at that proto-state and eventually led to its territorial demise.