Analysts say it will be more difficult for the United States or other Western powers to enforce a no-fly zone over Syria if Russia goes ahead with the sale of anti-aircraft missiles to its ally Damascus.
Moscow said this week it plans to deliver the advanced S-300 air defense system to the embattled government of Syrian President Bashar al-Assad, despite objections by the U.S., France and Israel.
Russian Deputy Foreign Minister Sergei Ryabkov said Tuesday the transfer will be a "stabilizing factor" and will deter what he called "some hotheads" from considering sending foreign forces to intervene in the Syrian conflict.
The surface-to-air missiles would represent a major upgrade over Syria's current air defenses and could challenge Western aircraft, said Ben MacQueen, a Middle East analyst at Australia's Monash University.
"The S-300 has the capacity to knock down cruise missiles as well as high-altitude planes," he said. "So the possession of the S-300 certainly does pose greater difficulties to a no-fly zone."
"It's not something that's likely to be a game changer in technical terms. If there were still a decision made to go ahead with a full-scale intervention, it's nothing that would repel those forces, but it changes the cost-benefit analysis for any sort of international coalition," said MacQueen.
The Obama administration has been reluctant to directly intervene in Syria. But some top U.S. lawmakers have been urging the White House to consider a no-fly zone to stop Syrian armed forces from carrying out air attacks that have killed a large number of both rebels and civilians during the over two-year-old conflict.
Russian officials are worried that a Western-imposed no-fly zone would end up like the one put in place by NATO over Libya in 2011, when longtime leader Moammar Gadhafi was overthrown with the support of foreign air power.
"NATO went well beyond that mandate, essentially becoming the air force for the rebel army," said University of San Francisco Middle East Studies professor Stephen Zunes. "And [the Russians] don't want to see a repeat of that. They don't want to see Western powers trying to impose their will on what has historically been allied with the Russians."
But some say the S-300 itself would not necessarily make the U.S. more reluctant to intervene. Even if Moscow goes ahead with the long-delayed sale, it could take up to two years before Syrian forces are able to effectively use the advanced Russian missile system, according to Middle East analyst Jonathan Adelman of the University of Denver.
"The Syrians don't know how to operate the S-300, and there's no way they're going to learn how to do it in an area as chaotic as Syria. So they're going to have to go to Moscow," he said. "Then they've got to bring it back and try and secure a place, because it's going to be immediately a tremendous focus of attention for the rebels and for the jihadists."
Another issue to consider, said Adelman, is whether Israel would intervene to stop the transfer of the S-300, which could challenge the dominance of Israeli air power in the region. It could also provide cover for the Syrian government to transfer weapons to the pro-Assad Lebanese militant group Hezbollah.
Israel's defense minister on Tuesday hinted at military action if the missiles are delivered.
"I hope they will not leave. And if, God forbid, they reach Syria, we will know what to do," said Moshe Yaalon.
Adelman said he has little doubt that Israel would take out the Russian missile system if it felt threatened.
"It's way up in the air whether this [system] is every going get there. If it gets there, is it ever going to get functional or is it going to get taken out by the Israelis or by forces on the ground? So I would argue that it's quite a destabilizing thing," he said.