Russia is the only country able to stop the Armenia-Azerbaijan conflict. Will it step up and do so?

People walk in a residential area of Stepanakert that was allegedly damaged by shelling on Saturday.

(CNN)For a while it seemed like they were friends. Russian President Vladimir Putin, the former KGB spy, had managed to slowly pry away one of NATO's most awkward members -- Turkish President Recep Tayyip Erdogan. The pair seemed always on the phone, Turkey was kicked out of the US-led F-35 program for buying Russia's S-400 air defense missile system, and Ankara seemed suddenly closer to Moscow than the Brussels-based alliance.

But how that has changed. After clashing in Syria, backing opposing sides in Libya, and generally finding the other an irritant in their respective bids to capitalize on America's regional withdrawal, Putin and Erdogan are no longer speed-dialing each other. In fact, with the ongoing and escalating fighting between Armenia and Azerbaijan over the enclave of Nagorno-Karabakh, Erdogan has left Putin in perhaps his most complicated spot in years.
Turkey's full-throated backing for the Azerbaijani campaign -- and quite possibly, its facilitation of Syrian mercenaries to back Azerbaijan, something Ankara officially denies -- has led Baku to some swift and brutal progress. Armenia has suggested reviving the old negotiations format, courted US support and vowed to fight on.
    But it does appear to be losing some ground. And as the shelling reaches civilian areas with greater frequency and depth on both sides, there is a deafening silence from Moscow. The regional powerbroker, which neighbors Azerbaijan but has a formal security alliance with Armenia, has used diplomacy to demand the guns fall silent, yet has so far watched this messy chapter in its backyard play out without its discernible influence.
    It is Moscow's move, really, this week.