DAMASCUS, Syria, Dec. 6 (UPI) --
Syria was poised to use the deadly sarin nerve agent against its own people Thursday after loading precursor chemicals into aerial bombs, U.S. officials said.
The bombs could be dropped on Syrians in "tactical bombings" from dozens of fighter-bombers, the officials told NBC News.
The regime's military awaited orders from embattled President Bashar Assad, said the network, whose report was corroborated by Fox News Channel.
A senior U.S. official told Fox News Syria had 60 days to use the bombs until the chemical mixture expired. At that point the bombs would have to be destroyed, the official said.
Syria is widely believed to have the world's largest stockpile of the non-conventional, banned weapons.
Syria also has access to extremely toxic tabun, the first nerve-agent chemical weapon discovered, as well as traditional chemical weapons such as mustard gas and extremely poisonous hydrogen cyanide.
U.S. Secretary of State Hillary Clinton Wednesday reiterated a U.S. warning to Assad not to use chemical weapons, saying at NATO headquarters in Brussels Washington and the 27 other NATO powers would consider such use crossing "a red line" that would lead to serious consequences.
U.S. President Barack Obama issued a similar warning Monday.
Clinton told reporters Wednesday the Assad regime was on the brink of collapse. "It is just a question of how many people have to die before that occurs," she said.
The entire NATO military alliance was therefore concerned "an increasingly desperate Assad regime might turn to chemical weapons, or might lose control of them to one of the many groups that are now operating within Syria," Clinton said.
"And so, as part of the absolute unity that we all have on this issue, we [the NATO countries] have sent an unmistakable message that this would cross a red line and those responsible would be held to account," she said.
NATO Secretary-General Anders Fogh Rasmussen warned the regime Tuesday any use of chemical arms would meet an "immediate" international response.
As recently as Tuesday, U.S. defense officials said they had no evidence Syria had begun mixing the precursor compound, which undergoes a chemical reaction to produce deadly sarin nerve gas.
But Wednesday, they said their worst fears had been confirmed -- the nerve agents were locked and loaded inside the bombs, NBC News said.
Sarin is classified as a weapon of mass destruction by the United Nations, and its production and stockpiling is outlawed under the 1993 Chemical Weapons Convention.
Syria is one of six nations that haven't ratified the convention. The others are Angola, North Korea, Egypt, Somalia and South Sudan.
Sarin is an extraordinarily lethal agent. Iraqi President Saddam Hussein's forces killed 3,200 to 5,000 Kurds with a single sarin attack on the Kurdish town of Halabja in Iraqi Kurdistan, 150 miles northeast of Baghdad, near the Iranian border.
That attack -- March 16, 1988, during the closing days of the Iran-Iraq war -- also injured 7,000 to 10,000 more, most of them civilians. Thousands more died of complications, diseases and birth defects in the years after the attack.
The attack was the largest chemical-weapons assault against a civilian area in history.
Clinton was expected next week to officially recognize the main Syrian opposition movement, the National Coalition of Syrian Revolutionary and Opposition Forces, when she meets with the so-called Friends of the Syrian People group in Morocco, NBC News said.
The coalition was created from a variety of opposition groups last month in a Doha, Qatar, meeting convened at the insistence of the United States and other nations.
"Now that there is a new opposition formed, we are going to be doing what we can to support that opposition," Clinton said. "I am looking forward to the Friends of the Syrian People meeting next week in Marrakesh, where we will explore with like-minded countries what we can do to bring this conflict to an end."
Britain, France, Turkey, Italy and Spain -- along with the Gulf Cooperation Council, representing Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates -- have already recognized the opposition.