By Barbara Starr

The Syrian president's control is crumbling at an accelerating pace but the latest assessment by U.S. intelligence finds few indications Bashar al-Assad is willing to step down, according to U.S. officials.

While Obama administration officials have said during the nearly two-year conflict that it appears al-Assad is weakened, the descriptions provided to CNN by U.S. officials familiar with the latest intelligence suggest the Syrian leader's problems have accelerated internally as the opposition continues to capture more territory.

"It's at its lowest point yet," said one senior U.S. official with direct knowledge of the latest assessments. U.S. intelligence believes the decline has accelerated in recent weeks. "The trend is moving more rapidly than it has in the past."

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The officials agreed to talk on the condition their names not be used because they were not authorized to discuss the information with the media.

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The description comes as a key Russian official suggested candidly that al-Assad could very well be defeated by the rising opposition fighters.

"The regime and the government in Syria are losing more and more control and more and more territory," Deputy Foreign Minister Mikhail Bodganov told a Russian government committee. "Unfortunately, we cannot rule out the victory of the Syrian opposition."

The remark was unusually frank from Moscow, given that until very recently Russia had publicly brushed aside suggestions al-Assad was losing control. Still, few think it will lead to a change in Russia's stance to block efforts to force him to leave government.

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Obama officials have publicly warned that al-Assad could resort to more drastic means to fight the opposition as he becomes more desperate.

Intelligence in recent weeks has found indications the Syrian military was mixing precursors for chemical weapons and loading them into bombs, though after public outcry and warnings from leaders around the globe there were signs that activity has "leveled off," according to Secretary of Defense Leon Panetta.

"But my concern is this: that as the opposition continues to move against the regime, particularly as they move towards Damascus, that if the regime feels that it's in danger of collapsing, that it might very well resort to these kinds of weapons. That's what concerns me the most," Panetta said in an interview this week with CNN's "Erin Burnett OutFront."

This week brought new concerns - that the Syrian military had fired Scud missiles at rebels, according to U.S. officials.

The White House spokesman said the use was a sign of al-Assad's "utter depravity" and a U.S. official said it could represent a "growing sense of desperation" by the government. But others within the U.S. government suggest the move might be more tactical than desperate.

If al-Assad is trying to keep his aircraft out of the range of opposition's surface-to-air missiles, the Scuds let him fire from much farther away and still reach into opposition territory, according to a U.S. intelligence assessment.

Syria's president is still controlling some of his military forces and commanders, but U.S. officials believe he and his top advisers are showing less ability to maintain control than they did six to eight months ago.

"There has been a strongly downward steady progression" in al-Assad's grip on power," said the senior U.S. official.

The United States believes "the wall around him is slowly coming down," said the senior official of the strong inner circle around al-Assad. "We are saying there are indicators there is weakening around Assad."

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That said, this senior official and other U.S. administration officials tell CNN that as of now there is no indication al-Assad is making plans to step down.

A second official said the leader and his commanders appear to be fully aware the opposition has made significant military gains in recent weeks and that Assad "is not out of it" in his understanding of the current situation.

The signs point to this conflict being resolved through fighting, not through a diplomatic or political solution, said a former U.S. ambassador to Syria.

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"My sense is that this will be ultimately decided through force of arms on the ground" - despite the Obama administration's reluctance to give heavy weapons to rebels, former Ambassador Frederic Hof told CNN's Christiane Amanpour on Wednesday.

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.

CNN's Jill Dougherty contributed to this report.