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.
Ben MacQueen, a Middle East analyst at Australia's Monash University tells VOA the surface-to-air missiles would represent a major upgrade over Syria's current air defenses and could challenge Western aircraft.
"The S-300 has the capacity to knock down cruise missiles as well as high-altitude planes. So the possession of the S-300 certainly does pose greater difficulties to a no-fly zone."
Some top U.S. lawmakers have been urging the Obama administration 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 two-year-old conflict.
Israel and the United States have urged Russia not to proceed with the sale, fearing the air defense system will threaten Israeli security and complicate any military action they may take in Syria.
Israeli Defense Minister Moshe Yaalon toughened that message Tuesday, warning of possible retaliation if the Russian missile technology is transferred.
"Obviously from our perspective it is a threat at this stage. I cannot affirm that things have been expedited. The shipments are not on their way yet, this I can say. I hope they will not leave and if, God forbid, they reach Syria, we will know what to do."
Western sources say Israel carried out several air strikes in Syria earlier this month, apparently to stop the Syrian government from transferring sophisticated weapons to the pro-Assad Lebanese militant group Hezbollah. Israel has neither confirmed nor denied responsibility for the strikes.
The Russian deputy foreign minister also criticized an EU decision to lift an arms embargo on the main opposition Syrian National Coalition while maintaining sanctions against the Syrian government.
Ryabkov accused the 27-nation bloc of "pouring more fuel on the fire" of Syria's civil war and "damaging" prospects for a U.S. and Russian-proposed peace conference to resolve the two-year conflict.
In separate remarks, Russian Foreign Minister Sergei Lavrov accused Western powers of carrying out a "whole range of actions" that undermine the idea of the conference.
Syria's foreign ministry issued a harsher criticism of the EU, accusing it of supporting "terrorists" in violation of international law and obstructing international efforts to find a political solution to the fighting.
The EU decided to lift the embargo on Syrian rebels at a meeting in Brussels on Monday. But, EU officials gave mixed messages about when such weapons transfers might begin.
Some officials said EU members agreed to delay any arming of the rebels until after August 1 to allow the U.S.-Russian peace initiative to proceed. But British and French officials said Tuesday there is no requirement to wait until August to send weapons, although they reiterated that their governments have no immediate plans to do so.
White House spokesman Jay Carney praised the EU action as a show of support for the Syrian opposition.
Syrian National Coalition spokesman Louay Safi also welcomed the lifting of the EU embargo as a "positive step," but warned that its impact may come too late to stop pro-Assad forces from killing civilians.