UN Special Envoy for Syria Staffan de Mistura has urged Russia to convince the Syrian government to reach a peace deal to end the nearly seven-year-old war.
De Mistura, speaking on Swiss television station RTS on December 13, said failure to make peace quickly through United Nations mediation could lead to "a fragmentation of Syria."
Russian President Vladimir Putin during a surprise visit to Russia's Hmeimim air base in Syria on December 11 declared that the work of Russian forces was largely done following the defeat of what he called "the most battle-hardened group of international terrorists."
With Russia signalling its hopes to conclude involvement in the Syrian conflict, De Mistura said Putin must "convince the [Syrian] government that there is no time to lose.... You can think you win territory militarily but you have to win the peace.
"And to win the peace, you have to have the courage to push the government to accept that there has to be a new constitution and new elections, through the United Nations," he said.
The nearly seven-year civil war in Syria has killed over 340,000 people and driven more than 11 million from their homes.
Diplomatic efforts to resolve the conflict have largely ended in failure over the opposition's demand that President Bashar al-Assad leave power, and the latest round due to end on December 14 in Geneva appears to be no exception.
Assad refuses to go, and recently has claimed he is close to military victory in the war, though his troops control only about 55 percent of Syria's territory after some recent gains.
The Kremlin first launched air strikes in Syria in September 2015 in its biggest Middle East intervention in decades, turning the tide of the conflict in Assad's favor.
Putin, like Assad, has portrayed their alliance as close to military victory, and Russia has insisted that Assad should be able to run for re-election during any political transition period negotiated by the UN.
Russia has offered to host a separate venue for peace negotiations. A parallel process organized by Moscow, fellow Syria ally Iran, and rebel-backer Turkey, has had limited success establishing cease-fires and is set to resume next week in Astana, Kazakhstan.
But De Mistura in the TV interview said that a lasting political settlement accepted by all sides can only be negotiated through the UN.
As in previous rounds of negotiations, the UN envoy in recent days has conducted shuttle diplomacy between the opposition delegation and the Syrian government delegation led by chief negotiator Bashar al-Ja'afari.
No direct talks between the two sides occurred.
"The opposition told me clearly when they arrived here, and again yesterday and this morning too, that they are ready to meet the government right away to have a hard, difficult discussion," De Mistura said.
"The government is not ready, it has said it is not ready to meet the opposition. That is regrettable but diplomacy has many means," he said.
A senior Western diplomat told Reuters that the government has been refusing to negotiate over a new constitution and elections.
"Clearly they did not have any intention to engage in this political process. And clearly they are not under sufficient pressure to do so," the diplomat told Reuters. "The clear impression is the regime wants to avoid the UN-led political process at any cost."
With reporting by AFP and Reuters