Hijab's public criticism of de Mistura, who must be seen as neutral while trying to negotiate peace in Syria, highlights the tensions and fragility of a peace process which has limped on despite the opposition declaring a "pause" in talks with nearly all of its delegation leaving Geneva.
"For two years, Mr de Mistura was appointed in his task as a UN envoy and during this period the killing was increased or doubled in Syria and also the number of villages and areas that were under siege also increased where is Mr De Mistura and his team," Hijab told reporters in Gaziantep where he was visiting a refugee camp alongside German Chancellor Angela Merkel and Prime Minister Ahmet Davutoglu, Reuters reported.
Despite a breakdown in a truce, the failure of which Hijab said must prompt a reevaluation by world powers, and signs that both sides are gearing up to escalate the five-year-old civil war, De Mistura vowed to plough on with peace talks.
Some diplomats called on de Mistura to exert pressure to make the talks successful.