>>>President Barack Obama says the United States has evidence chemical weapons were used in Syria, but more proof is needed before he would order an American response.  Analysts say if the Syrian government used such weapons, it would fit a pattern of gradual escalation of the attacks against rebel forces during the two-year long civil war.

U.S. intelligence agencies believe it is likely the Syrian government has used the lethal nerve agent sarin.

But President Obama says the evidence is not strong enough for the U.S. to take action.

"What we now have is evidence that chemical weapons have been used inside of Syria but we don't know how they were used, when they were used, who used them," said President Obama.

Some analysts believe using only a small amount of these weapons is designed to avoid mass casualties and is a strategic decision by Syrian President Bashar al-Assad.

Joseph Holliday is a former intelligence officer in the U.S. Army who is now a senior research analyst at the Institute for the Study of War.

“And so this careful introduction is designed to ensure that there is not a major reaction, which will allow him to ratchet up the use of the [chemical] weapons in the future," said Holliday.

The commander of the Free Syrian Army, General Salim Idris, said in a letter to President Obama that the Assad government's use of chemical weapons could be a prelude to a larger deployment of such weapons as part of that government's strategy.

The subtle introduction of chemical weapons appears to fit the Assad government’s model for military escalation.

After using heavy artillery to shell rebel-held cities, the government deployed helicopter gunships and then Syrian war planes.

The Syrian military even fired Scud missiles into densely populated urban areas.

“I think that Assad has been able to call our bluff in many respects because there really are not many good options for military intervention in Syria," Holiday said.

The Assad government blames recent bombings in Damascus on terrorists, a term officials use to describe rebel fighters. And it has denied using chemical weapons.

"If they had any proof, any evidence, any tools - credible - they should share it with the secretary-general.  They should share it with us," said Syria’s U.N. Ambassador is Bashar Jaafari:

Analysts say chemical weapons are part of the government’s strategy of forcing civilians to flee rebel held areas without the destruction of infrastructure caused by conventional weapons.

They say this ensures that even when rebels capture territory they lose much of the population.

“I think we are looking at potentially a quarter of the Syrian population has either been displaced within their cities, out of their cities, or even across international borders," Holliday said.

The Free Syrian Army is asking the U.S. to help rid Syria of the Assad government and its chemical weapons.