No doubt about it, this is an escalation. And a dangerous one at that.

New York Times:

President Bashar al-Assad's forces have resorted to firing ballistic missiles at rebel fighters inside Syria, Obama administration officials said Wednesday, escalating a nearly two-year-old civil war as the government struggles to slow the momentum of a gaining insurgency.

Administration officials said that over the last week, Assad forces for the first time had fired at least six Soviet-designed Scud missiles in the latest bid to push back rebels who have consistently chipped away at the government's military superiority.

In a conflict that has already killed more than 40,000 Syrians, the government has been forced to augment its reliance on troops with artillery, then air power and now missiles as the rebels have taken over military bases and closed in on the capital, Damascus. The escalation has not changed Washington's decision to avoid military intervention in Syria - as long as chemical weapons are not used - but it did prompt a rebuke.

"As the regime becomes more and more desperate, we see it resorting to increased lethality and more vicious weapons moving forward, and we have in recent days seen missiles deployed," said Victoria Nuland, a State Department spokeswoman.

President Obama has said that the use of chemical weapons would cross a "red line," implying that it might lead to an American military response.

Mr. Assad's decision to fire Scuds - not known for their precision - inside his own country appears directly related to the rebel ability to take command of military bases and seize antiaircraft weapons. The Scuds have been fired since Monday from the An Nasiriyah Air Base, north of Damascus, according to American officials familiar with the classified intelligence reports about the attacks. The target was the Sheikh Suleiman base north of Aleppo, which rebel forces had occupied.

Jonathan Spyer writing at PJ Media describes the beginnings of the battle for Damascus:

With much of the north and east of Syria now in the hands of the insurgency, Assad has strengthened his defenses in the largely Alawi western coastal region.  His troops are maintaining a defensive line at the eastern edge of this region, along the Orontes River Valley, west of the largely Sunni cities of Homs and Hama.  This line must be maintained, in order to keep open the link between Damascus and the emergent Alawi enclave in the west.

If the capital falls, Bashar Assad will effectively lose any claim to be the ruler of Syria. Instead, he (or perhaps another senior Alawi figure) will become the leader of a particularly well-armed sectarian militia.

This militia will then seek to defend its heartland in the west. The Sunni rebels, meanwhile, will seek to reconquer and destroy the Alawi enclave. They will be faced with a similar task in the Kurdish north east of the country.

So the Assad regime's support base is shrinking down to its sectarian core - namely, the 12% Alawi minority from which the ruling family comes.

This narrow base has proved the regime's Achilles heel. It has forced the regime to abandon large swathes of the country and construct ever narrower defensive lines, which it has the manpower to defend.

But the ethnic nature of the regime's support means that rather than simply melting away, its base has narrowed down to a hard, solid essence. The men remaining with Assad are united not just by coercion, but by fear of what is in store for themselves and their families should the Sunni Islamism of the rebels triumph.

They will fight for every inch of ground.  They may succeed in holding the center of Damascus for quite a while yet. But even when the city falls, this will not mean the end of their war.

Spyer doesn't think the use of chemical weapons by Assad is imminent, but he points out the greater danger of rebel factions allied with al-Qaeda getting their hands on WMD. That would be catastrophic for the US and the west.

The end game in Syria is in sight, but it will take a long time to get there.