The group "will leave Geneva tomorrow (Thursday) and will not return until the humanitarian demands are met or (we) see something on the ground," Hijab told reporters.
The High Negotiations Committee "came (to Geneva) because of these assurances. But the opposite happened," he said. "Nothing happened on the humanitarian front and the regime caused the political process to fail."
"Unfortunately whenever there is a political process that starts the regime feels threatened and uses these kinds of tactics," he said.
"The whole world sees who is making the negotiations fail. Who is bombing civilians and starving people to death."
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In a separate news conference, chief government negotiator Bashar al-Jaafari put the blame on opposition "preconditions" for the failure.
"Since its arrival... (the HNC) refused to take part in any serious talks with the (UN) special envoy," state news agency SANA quoted Jaafari as saying.
UN special envoy Staffan de Mistura said earlier Saturday that the "temporary pause" was needed because there is "more work to be done, not only by us but the stakeholders," referring to outside powers embroiled in the conflict.
"It is not the end or the failure of the talks," he said.
The comments came after several days of fruitless talks during which de Mistura tried to coax the Syrian government and opposition into beginning six months of indirect talks.