In response to Britain and France lifting the embargo on arming the Syrian rebels, Russia has announced it's going ahead with selling a very potent anti-aircraft system to the Syrian government. This probably means no U.S. intervention:
Russia will deliver an advanced air defense system to the Syrian government despite Western opposition because it will help deter "hotheads" who back foreign intervention, a senior Russian official said on Tuesday. ...
The S-300s can intercept manned aircraft and guided missiles and their delivery would improve Assad's government's chances of holding out in Damascus.
It ranges 125 miles a shot; and can shoot down missiles as well as fighter planes. However unenthusiastic the U.S. military is about a no-fly zone right now, confronting the S-300 would make it instantly worried about losing many, many pilots. “This is a system that scares every Western air force,” Lexington Institute defense analyst Dan Goure once remarked.
The U.S. obviously prefers to use airpower instead of ground forces because, usually, America can establish complete air superiority, virtually eliminating the chance of taking casualties. The S-300 would make that impossible. Manned fighters and bombers, drones, and cruise missiles would all be vulnerable, even if they were attacking targets in Syria while operating outside of its airspace. Combine that with the fact that Russia recently gave Assad sophisticated anti-ship missiles which can hit targets over 180 miles away, and it means the U.S. will not want to risk its carriers in the Mediterranean.
If the idea on the part of Britain and France was to arm the rebels while they and the U.S. provided air cover, they will have to think again.
This is all of a piece with Assad's apparent strategy of taking every opportunity to show the West that he has the upper hand. He crossed the so-called "red line" by using chemical weapons, and when nothing happened, he started using them more. Sen. McCain made a brief trip into the country to meet with rebel leaders, and it's obvious McCain - one of the "hotheads" Russia is talking about - will bang the war drum for American intervention by citing chemical weapons use when he gets back. Assad's spokesmen have been constantly referring to the rebels as terrorists and "al Qaeda" and playing up atrocities - like a rebel posting video of himself eating a human heart - to drive down Western public support for intervention.