Last weekend, the Russian foreign minister and American secretary of state met in Geneva, with the United Nations-Arab League envoy to Syria, Lakhdar Brahimi. Russian foreign minister Sergey Lavrov denied that Moscow was discussing a transition away from President Bashar Al Assad or had softened its position on Syria. "All attempts to portray things differently are unscrupulous," Mr Lavrov said.
The portrayals were not so much unscrupulous as tending to look at only half of the picture. There is another country with power in Syria that cannot be overlooked in a final settlement, namely Iran. For as long as Iranian support counts with the regime of Mr Al Assad, Russia and other outside powers will find it difficult to reach agreement on the future of the Syrian regime.
Influence lasts for as long as one can play the diplomatic game. Iran, like Russia, fears that too sudden a downfall of the Syrian president would undermine its Syrian stakes. These are most pronounced in the military-intelligence apparatus, which for decades has allowed Iran to reinforce its strategic presence in the Levant, above all in Lebanon.
Were Iran to lose its Syrian ally, its interests in the eastern Mediterranean would be greatly harmed. Tehran's ability to bolster Hizbollah in a time of war would be crippled, limiting Iran's and the party's deterrence capability. Hizbollah would find itself isolated in Lebanon, surrounded by an unfriendly Sunni community at home and in Syria. The party would be much less able to strike back at Israel in the event of an Israeli attack on Iran's nuclear facilities.
That is why Iranian officials have sought to protect Syria's military-security network. An Iranian politician, Hamidreza Taragh, made this clear when he told The New York Times this week: "But whatever the cost [of a peaceful solution through political reform in Syria], we want to keep Syria in the group of resistance against Israel."
"Resistance" is shorthand for maintaining Syria's military capability. Security figures in Tehran realise that it is in the armed forces and intelligence services, top-heavy with members of Mr Al Assad's minority Alawite sect, that they will continue to have a say. The rebels, in turn, have no incentive to side with Iran if they triumph, both from a sectarian perspective and because they cannot afford to alienate the Gulf states before a costly post-war reconstruction effort.
Reports from pro-Syrian figures in Beirut show the extent of Iranian involvement in the regime's operations. Apparently, Iran has played a leading role in planning the regime's counter-attack around Damascus, to push the rebels out of the capital and diminish their ability to surround the city. Iran still believes that Mr Al Assad can survive politically, but feel his military must regain the initiative.
If that's the thinking, the Iranians may be disappointed. Nothing suggests that the Syrian regime is making significant headway around Damascus. Instead, there is more wanton violence. If the aim is for the regime to show that it is solid and has a plan in the capital, it will have to do better than replicate the butchery of the past months.
Some observers wonder whether the Syrian army is too exhausted to do what the Iranians want. The army has remained unified and still has substantial weaponry. Yet there is a prevailing sense that it has permanently lost the initiative. Such a perception of steady reversal can only lose the regime the backing of powerful domestic actors, above all economic actors, who can help it to survive.
In major challenges to the regime, such as recapturing Aleppo and maintaining an open supply line to units in northern Syria, Mr Al Assad has come up short. Moreover, the president has been unable to progress in his strategy of last year, namely to use military might to force the opposition to come to the negotiating table and accept a disadvantageous deal. Iran appears to feel there is still room for this outcome, but other countries are more sceptical.
Mr Al Assad may not be about to fall, but his worries must have suddenly redoubled. A desirable scenario for many governments is that members of the Alawite officer corps will oust the president, and in exchange will win assurances that they will be able to retain authority in a post-war order. However, there would be much uncertainty involved. It would divide the Alawites and probably bring few concessions from the Syrian opposition.
Iranian backing is essential in that regard. If there is one thing that Iran can do, it's to keep an eye on the mood among senior Syrian officers, and so protect Mr Al Assad. Despite its talk of political reforms, Iran seems profoundly reluctant to find a solution that involves sacrificing the Syrian president. His removal could send an unwanted message homeward, where the leadership has employed repression when change from the street has seemed possible.
Iran's limited margin of manoeuvre in Syria is not enviable. The Islamic Republic is playing a game of double or nothing. Either Mr Al Assad wins, or he loses everything, and with him all those who have been fortifying his regime in the past 21 months. But it is improbable that he will win, which means Iran is virtually ensuring that a post-revolutionary Syria opposes Tehran.
This has led to speculation that Iran will destabilise a Syria it cannot control. Better chaos than letting the Syria prize fall into the hands of its enemies, the rationale goes. However, this could facilitate Syria's fragmentation, and possibly that of Iraq and of Lebanon, harming Iranian allies there. Iran has placed all its chips on Mr Al Assad, and this could backfire. For what the Iranians want to preserve is the hated core of his regime, which most Syrians cannot accept.
Michael Young is opinion editor of The Daily Star newspaper in Beirut
On Twitter: @BeirutCalling.