The war in Syria has been raging for nearly four years and it's been challenging for diplomats to get warring sides to agree on even temporary truces.
The U.N. envoy is pressing ahead on that front, while Russia tries to play peacemaker. Russia is inviting the parties to Moscow this month, but some opposition groups won't go to a country that has been backing Syrian President Bashar al-Assad.
Syrian opposition figures have good reason to be skeptical of Moscow's diplomatic moves, says Reza Afshar, a former British diplomat who now works for Independent Diplomat, a diplomatic advisory group, and advises the Syrian opposition coalition.
"A process that is initiated by the Russians, who are a party to the conflict — they provide weapons and advice to the Assad regime and they have taken an approach of cherry-picking who they talk to and who the regime talks to — is obviously a process that is going to be concerning to some people, of course," Afshar says.
The U.S. is not pressuring the opposition groups it supports to go to Moscow. Instead it's suggesting they should think about it so that Russia can't blame the opposition for the diplomatic stalemate. From the U.S. perspective, the opposition has nothing to lose by going, but National Defense University professor Murhaf Jouejati disagrees.
"If there are no guarantees as to the end state, that is, a movement towards a transitional government with full executive powers without Assad, then there is really no reason to go," he says. "It will only be a repeat of the failed Geneva talks."
Russia's ambassador to the U.N., Vitaly Churkin, says the meetings, set to begin Jan. 26 in Moscow, are meant to revive the peace process that started in Geneva in 2012.
"Those who decide not to take part in this event will lose their standing in the entire negotiation process," he said on the floor of the Security Council.
That warning won't work with Syrian opposition groups, Afshar says.
"Well, that's typical Russian behavior, which is to try to bully and threaten people," he says. "But the reality is, the Russians aren't in a position to decide who will take part in future negotiations. And this has been the whole problem with their approach."
He says the Russian job has always been to deliver the regime to the negotiating table, but the Syrian government only wants to talk about fighting terrorism, not discuss a political transition. So international diplomats, even U.N. envoy Staffan de Mistura, aren't raising expectations about this month's meeting in Moscow.
"We are hoping, more than expecting, that it will be a success," he says.
De Mistura describes Syria as the largest humanitarian crisis since World War II, and he's been meeting U.S. and Russian officials, plus many others, to find ways to resolve this.
"They all agree that we need to do something to avoid that the Syrian conflict goes into a back burner and that movement towards some type of political solution should take place this year," he says.
That optimism isn't shared by Professor Jouejati, who points out that the U.N. envoy has had trouble getting the warring sides to agree to a temporary truce in the city of Aleppo. He says that's because Assad thinks he's winning — and U.S. plans to train and equip 5,000 moderate rebels a year won't help level the playing field.
"De Mistura has a lot of energy and a lot of good will," Jouejati says, "but I think the realities on the ground are quite difficult."
There are other complicating factors, too. The rise of the self-proclaimed Islamic State and the U.S.-led airstrikes against that group in both Syria and Iraq now top the U.S. agenda.