A political deal to end the Syrian conflict is not possible without a strong US role, the opposition's chief negotiator told AFP, warning that Washington's absence was threatening ongoing peace talks.
Lead negotiator for the main opposition High Negotiations Committee (HNC), Mohamad Sabra, said in an interview late Monday that the UN-backed talks in Geneva remained "stalled".
"There can be no real and viable political solution without the presence of the Americans," he said.
The United States has a "moral duty" to throw its weight behind efforts to end the six-year conflict, he added.
Years of diplomatic initiatives have failed to end the war, which has killed more than 320,000 people and displaced millions since it started in March 2011 with protests against President Bashar al-Assad's regime.
Washington has long been the biggest backer of the Syrian opposition, but it appears to be putting far less diplomatic muscle towards the rebel cause since President Donald Trump came to power in January.
Two UN-backed taskforces co-chaired by the United States and Russia and aimed at securing ceasefires and access for humanitarian aid in Syria seem to be having less impact.
At the same time, regime supporters Russia and Iran along with rebel-backer Turkey have been pushing separate negotiations in Astana since January after gains on the ground by Damascus turned the tables in the conflict.
Russian President Vladimir Putin was on Tuesday set to host his Iranian counterpart Hassan Rouhani for talks that are being closely watched for signs of their next moves in Syria.
Closer cooperation between the two Syrian regime supporters will likely go even further in marginalising US influence in the peace process.
- 'No partner' -
While urging Washington to be more fully engaged in the peace process, Sabra warned that a deal would be impossible "if the Russians do not withdraw their (military) support for the regime."
Russia's entry into the conflict in September 2015 -- when it began launching air strikes to shore up Assad's forces -- played a significant role in turning the tide for the Syrian regime.
The HNC delegation was expected to meet with Russian Deputy Foreign Minister Genady Gatilov on Wednesday, after he met with the government delegation on Tuesday.
In the interview, Sabra also reiterated the HNC's often-repeated claim that the Syrian government delegation, headed by the country's ambassador to the UN Bashar al-Jaafari, was "not seriously involved" in the talks.
"Until now, we don't have a partner in these negotiations," he insisted.
His comments came amid a fifth round of negotiations in Geneva being mediated by UN Special Envoy Staffan de Mistura which have remained clouded by persistent violence on the ground and deadlock over the country's political future.
The government has ruled out discussing Assad's possible departure, while the HNC says it will refuse any deal that leaves him in power.
Sabra insisted that "once the transitional government is formed," Assad's regime would end, and he "and his clique will be referred to a fair trial" for their crimes.