Given that, the continuing concern is a sudden implosion of the Syrian government and a resulting security vacuum. The senior official said the United States feels it has enough intelligence indicators to be aware when that may happen.
Even with the rebel advances, the Syrian military forces that have stayed to fight for the government appear to be holding firm in their loyalty. There are signs that military defections at the commander level are slowing, though the U.S. analysts are not sure why, according to a second U.S. official.
"There is still regime control over the military despite the fact they recognize the opposition force has improved," said the second U.S. official, also directly familiar with the latest assessment on Syria said.
It could be the major period of defections is over, or there is tighter security. There continues to be some defections, especially of lower level troops, the second official said.