Syria has armed dozens of bombs with sarin gas and other chemical weapons that could be used to target opposition less than two hours after President Bashar al-Assad issues orders, US officials have claimed.
Only concerted diplomatic pressure from the US, Russia, China and other countries has stopped the regime from loading the bombs on to its aircraft.
Satellite imagery gathered by Israel and other states in late November showed regime soldiers preparing the 500lb bombs in late November.
The intelligence triggered a public warning from Leon Panetta, the US Defence Secretary, that the regime would cross a "red line" triggering military intervention if it used the bombs.
Diplomats told The New York Times that American, European, Arab diplomats hurriedly coordinated warnings to Damascus to stop preparing the devices.
But America and its allies remain concerned that the bombs could be dropped by the regime at short notice.
The effectiveness of the weapons would depend on weather conditions and the terrain.
The US military has deployed 150 specialist officers to Jordan to monitor and respond to a chemical weapons attack by the regime.
Meanwhile it was reported that almost 100,000 people fled the Syrian civil war in the last month.
There are now almost 600,000 refugees living outside Syria.
Tens of thousands more have fled the country but not felt the need to register as refugees.
Ban Ki-moon, the UN Secretary General, has accused President Assad of sabotaging a UN-sponsored peace initiative.
"What the Syrian people desperately need at this time are real solutions to the crisis that is tearing their nation apart," Mr Ban said through his spokesman.
The UN leader criticised Assad for having "rejected the most important element" of a June 30 road map agreed by the main powers in Geneva that called for a political transition with the establishment of a transitional governing body.
"The United Nations remains committed to do its utmost, in co-operation with other partners, to alleviate the suffering of the Syrian people inside and outside Syria," the spokesman said.
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