Implied in those warnings is the threat of some sort of military action, which itself presents a number of options, challenges and risks, foreign affairs analysts say.
On Tuesday, U.S. Defence Secretary Leon Panetta indicated that Syria's Bashar al-Assad regime may be heeding these warnings from the international community and appears to have slowed preparations for the possible deployment of chemical weapons.
Last week U.S. officials said there was evidence that Syrian forces had begun preparing sarin gas for possible use in bombs. Syria is said to have one of the world's biggest stockpiles of the deadly gas.
Still, the international concern regarding Syria's chemical weapons remains high, and means that contingency plans are still being developed to attack suspected sites if Assad ever decides to unleash his arsenal.
If Western powers do respond, "they have to act fast and the way they can do that is basically two options: either through air strikes or cruise missile strikes," said Omar Lamrani, a military analyst for Stratfor, a global intelligence company. Those two choices, he said, represent "the safest option."
Although an air or missile strike would lessen U.S casualties, Lamrani said it could also increase the risk of contaminating those sites where chemical weapons are stored.
"Blowing up these areas, a lot of the material may be incinerated but there will still be significant risk of leaks and gas clouds," he said.
Regime's arsenal believed to contain sarin
According to a Stratfor analysis, the regime's chemical arsenal is believed to contain sarin, VX, tabun and mustard gas, with one source estimating 650 metric tonnes of sarin and 200 metric tonnes of mustard gas.
The weapons, scattered around dozens of sites, could be deployed from artillery, aircraft and ballistic missiles, including different types of Scud missiles.
The Syrian government has never confirmed it has chemical weapons, but has insisted it would never use such weapons against its own people.
Syria is not a signatory to the 1997 Convention on Chemical Weapons and thus is not obliged to permit international inspection.
If the West suspects chemical weapons are being introduced to the battlefield, it would also likely hit hard at regime elements and regime leadership, to break down the command and control infrastructure and prevent the coordination of any chemical weapon attacks, Lamrani said.
Christopher Chivvis, senior political scientist of RAND corporation, a global policy think tank, said the U.S. would also want to do something that both helps the opposition and penalizes the regime.
"So you could see something like an effort to destroy Assad's airforce. You could see that in combination with destruction of Assad's integrated air defence system, along with the establishment of a no-flight and no-drive zone."
But none of this guarantees that all the chemical weapons stockpiles would be destroyed, or that the remaining weapons wouldn't fall into the hands of some al-Qaeda linked groups, which are also in Syria fighting on the rebel side.
If this fear were strongly held, it would likely necessitate the more risky and least politically palatable option of sending in ground troops.
Possibility of ground troops
The Pentagon has estimated that around 75,000 troops would be needed to secure the entire chemical warfare infrastructure for Syria.
"They would have to go in with transport aircraft, they’d have to go onto the ground, fight their way into the facilities that no one really knows how they are laid out," Lamrani said. "You need a lot of expertise in actually securing the material."
Anthony Cordesman, an analyst at the Centre for Strategic and International Studies in Washington, said in an interview with the Voice of America that those troops would have to battle the elite Syrian forces assigned to guard the chemical weapons sites.
Cordesman said most of those sites are "heavily defended" by Assad loyalists. He added that Syria's sophisticated air defences also could pose a threat to an aerial commando strategy.
"There is no way you can move aircraft into the areas without being detected by radar. So even special forces raids could have serious problems just in getting to a facility undetected."
Thomas Donnelly, a defence and security policy analyst for the American Enterprise Institute, said another challenge would be securing weapons that are not at the sites, but have been deployed to specific regime troops.
"As the weapons move from central storage facilities to units in the field, the military tasks grow and grow exponentially, just finding all those things in a timely way," he said.
Canada still shy of commitment
Then, there are the geo-political considerations and the questions of what countries would be involved in such an effort to respond against Syria.
On Tuesday, Foreign Affairs Minister John Baird stopped short of confirming that Canada would use its military to be part of a NATO force if Syria resorts to chemical weapon use, but suggested that Canada likely would be part of an international coalition.
"It's very unlikely [the U.S.] would do it in an unilateral capacity," Chivvis said. "[They'd] try to get regional powers, Turkey and Saudi Arabia and other Gulf states involved, with U.S providing … specific tasks that need to be done to secure the chemical weapons."
With up to 40,000 Syrians believed to have been killed since the uprising against Assad began in March 2011, some may question why the use of chemical weapons would be the trigger for U.S. involvement.
But Chivvis said there's "symbolic damage" to allow a country to use these weapons.
"To date, there's been a pretty strong taboo on the use of chemical weapons over the course of the last century. They have been used from time to time, in the Iran-Iraq war most significantly, but in general there's been a taboo on using them.
"So anything that would break that taboo could mean a very different kind of security context in the future. So there are good reasons to deter a regime like the Assad regime from using them."Suggest a correction