Syrian President Bashar al-Assad’s continued survival is predicated on their Russian patrons to a large extent. So this shift from Moscow is really a crushing blow:

Russia will cease deliveries of arms and fighter planes to Syria until the situation in the country stabilises, an official said yesterday, a move that would ratchet up pressure significantly on Bashar al-Assad’s regime.

The announcement is the strongest signal yet of Russia’s hardening stance against its long-time ally, and will come as a blow to the Syrian president, who yesterday met with Kofi Annan to discuss a political initiative to bring an end to the crisis. The UN-Arab League envoy expressed optimism after the talks, saying he and Assad had “agreed on an approach” to end the bloodshed, which he would take to the opposition.

Annan did meet with Assad yesterday, and tried to enlist Iran and Iraq in his efforts to arrive at a peaceful transition today. But really, the best hope for a resolution lies with Russia getting tough. This potential denial of arms shipments would do the trick. But right now, only a deputy director, a midlevel military official, is on the record. Until I hear this from Vladimir Putin or his foreign minister, and until the shipments actually stop, I’m skeptical.

The foreign minister, Sergei Lavrov, did meet with a Syrian opposition leader yesterday in Moscow, so that’s a more hopeful sign. For some reason Lavrov said he was working to implement the Annan plan, which is clearly inoperative at this point. But the symbolism of the meeting itself is significant.

Annan’s latest plan, which he said had agreement from Assad, is to stop the violence in the most violent areas, and then extend the cease-fire to the rest of the country. But nothing has really worked on this front yet. If you want to know when Assad will go, look to Moscow.