According to Hillary Clinton, a delivery of helicopter gunships is on its way from Russia to President Bashar Al-Assad in Syria. If so, any prospect of a managed end to the bloodshed there is dwindling fast, and Russia will bear responsibility.

Foreign military intervention will eventually come if diplomacy fails. The only questions will be when, what form that intervention will take and who will carry it out. In the meantime, many thousands more Syrians will likely die.

Clinton, the U.S. secretary of state, did not reveal details of the alleged shipment and a Bloomberg News report, citing Russian officials, suggests the helicopters in question are part of a four-year-old contract to refurbish 20 Mi-24 gunships that Syria bought long ago. Whether these choppers are new or refurbished is irrelevant. At a time when the regime in Damascus has just started using combat helicopters to attack its domestic opponents, it’s troubling that Russia would be choosing to send more.

Putin’s statement just a week ago, that his country wasn’t supplying any arms to Assad that could be used domestically, now appears breathtaking in its cynicism. Foreign Minister Sergei Lavrov said Wednesday in response to Clinton that Russia was only supplying air defense equipment against an external attack. We’re sorry, helicopter gunships don’t count.

Bloomberg View was an early proponent of efforts by the U.S. administration and United Nations-Arab League envoy Kofi Annan to persuade Russia’s leadership to cooperate in effecting a Yemen-style transition in Syria. Under such an arrangement, Assad would leave power and those left behind would negotiate a political settlement. Russia would play a significant role in that process and its aftermath.

We still believe this would be the best way to save lives in Syria and to ensure against contagion in a rolling sectarian conflict between Sunnis and Shiites that could destabilize the region. Talks snagged over Russia’s demand that Iran, Syria’s No. 1 backer, should be at the table. But if Russia’s response to such overtures is to resupply Assad with attack helicopters, the attempt is clearly doomed.

Putin, it’s worth remembering, does not believe in popular uprisings, at home and abroad. He appears to be convinced that the Arab Spring was inspired, organized and manipulated by the West, to Russia’s strategic detriment. This view disregards the rights and choices of millions of individuals from Tunisia to Syria. It also, apparently, outweighs the reputational and diplomatic costs of aiding butchery in Syria.

There are, of course, two sides to this conflict. The pace of fighting increased significantly in recent weeks, as anti-tank weapons -- purchased with money from Saudi Arabia and Qatar -- arrived in rebel hands. Those weapons quickly took a toll on a Syrian army that had been able to operate with near impunity. It’s hard to quibble with the right of rebel forces to fight back with the best weapons they can get. But the escalation involved has demonstrated some of the risks that have caused us to oppose arming the opposition.

It is no coincidence that some of the worst atrocities of the conflict to date have taken place in step with this arms escalation. Nor is it a coincidence that the regime has, for the first time, deployed combat helicopters, as confirmed by Annan’s UN observers. That’s a logical, if lamentable, step for Syria’s military to take once its tanks have become vulnerable to attack.

An article in the Wall Street Journal on Wednesday traced a pattern of refugee accusations and movements on the ground that suggest the Syrian military is trying to clear safe, homogenous zones for Syria’s 10 percent Alawite minority along the coast, with a corridor to the capital, Damascus. Such planned ethnic cleansing is all too reminiscent of the 1992-1995 war in Bosnia, where about 100,000 people died in a country with less than a fifth of Syria’s population.

Syria has not yet sunk so deep, but it could get there. The last best chance to arrest the fall comes next week in Mexico at the Group of 20 summit. There, President Barack Obama and others need to make the case to Putin that sending Assad more combat helicopters will guarantee not a Syrian government victory but a further arms escalation, probably in the form of shoulder-held anti-aircraft weapons sold to the rebels to shoot down gunships newly arrived from Russia.

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