Syria on Thursday accused the main opposition of taking UN-backed peace talks "hostage" over its refusal to include terrorism on the agenda, warning it would be reponsible if the sputtering negotiations fail.
Russia, a key ally of Damascus, also attacked the opposition led by the High Negotiations Committee, which said it was pinning its faltering hopes on the new US administration of President Donald Trump.
"Progress in the Geneva round must not be held hostage by the Riyadh platform," lead Syrian negotiator Bashar al-Jaafari told reporters, referring to the Saudi-backed HNC.
Speaking after confirming that Syrian forces had "liberated" the historic city of Palmyra from the Islamic State group, he said the opposition "will be responsible for any failure of the Geneva talks".
The HNC said Wednesday that terrorism could not be added to the faltering talks, launched by UN envoy Staffan de Mistura last Thursday and which are expected to stumble to an end by this weekend despite few signs of progress.
The opposition has charged that Damascus fixates on the role of jihadists in the conflict to distract from discussions on political transition and organising elections in the war-ravaged country.
"We will not deal with it, and if (de Mistura) adds it in any time we will not deal with it or discuss it," HNC delegation chief Yehya Kodmani told reporters on Wednesday.
Jaafari said that answer "did not come as a surprise", in part because "a lot of the members of the HNC are considered terrorists", a charge he has levelled in previous rounds.
The issue has overshadowed the Geneva talks, in particular after a suicide assault in Syria's third-largest city of Homs last weekend which killed dozens of people.
Earlier Thursday in Moscow a Russian foreign ministry spokeswoman accused the Syrian opposition of "sabotaging" the Geneva talks.
"The results of the first days of the intra-Syrian dialogues, as before, raise questions over the ability of the Syrian opposition representatives to reach a deal," said spokeswoman Maria Zakharova.
She added that the HNC's refusal to cooperate on an equal footing with two Russian-backed groups meant that it was "de facto sabotaging the full dialogue with both the Syrian government delegation and with other opposition groups".
Speaking late Wednesday in Geneva, the HNC said it is counting on the new US Trump administration to play a "positive" role after "catastrophic" policy mistakes under his predecessor Barack Obama.
"We are here to... send a message to the new American administration which is trying... to fight terrorism, that we are the side working for peace and security in Syria," said HNC delegation chief Nasr al-Hariri.
"The Syrian people are paying the price because of the Obama administration's catastrophic mistakes," he told a small group of journalists.