(CNN) -- Here is a history of U.S. and Western warnings against the use of chemical weapons by Syria, where a 2-year-old civil war has left more than 70,000 people dead, according to estimates. Military analysts believe Syria may have one of the largest stockpiles of chemical weapons in the world.
July 13, 2012
A U.S. official, speaking on condition of anonymity, tells CNN that Syria is believed to have moved some of its chemical weapons in recent days. U.S. State Department spokeswoman Victoria Nuland tells reporters it is Syria's responsibility to safeguard those long-suspected stockpiles "and that the international community will hold accountable any Syrian officials who fail to meet that obligation."
July 23, 2012
-- Syrian Foreign Ministry spokesman Jihad Makdissi confirms for the first time that Damascus has "unconventional" weapons but vows they "would never be used against civilians or against the Syrian people during this crisis at any circumstance."
"All the stocks of these weapons that the Syrian Arab Republic possesses are monitored and guarded by the Syrian army. These weapons are meant to be used only and strictly in the event of external aggression against the Syrian Arab Republic," Makdissi says.
-- Speaking to a Veterans of Foreign Wars convention in Nevada, President Barack Obama says the United States "will continue to make it clear" to embattled Syrian President Bashar al-Assad and his top aides "that the world is watching, and that they will be held accountable by the international community and the United States should they make the tragic mistake of using those weapons."
August 20, 2012
Obama calls the movement or use of chemical or biological weapons in Syria a "red line" that could cause him to dispatch U.S. forces into the conflict.
"We cannot have a situation where chemical or biological weapons are falling into the hands of the wrong people," Obama tells reporters at the White House. He adds, "We have communicated in no uncertain terms with every player in the region that that's a red line for us and that there would be enormous consequences if we start seeing movement on the chemical weapons front or the use of chemical weapons."
August 23, 2012
Britain and the United States would "revisit their approach" to Syria if the Syrian government used chemical weapons, British Prime Minister David Cameron's office says. Cameron and Obama agree that the use of chemical weapons would be "completely unacceptable," 10 Downing Street announces.
August 28, 2012
French President Francois Hollande says the use of chemical weapons by the Syrian regime "would be a legitimate reason for direct intervention" in the conflict.
September 28, 2012
A former Syrian major general says Syria could "easily" transfer chemical munitions to its Lebanese ally, the Shiite Muslim militia Hezbollah if it feared the weapons were to fall into rebel hands.
October 12, 2012
U.S. Defense Secretary Leon Panetta says Washington has sent roughly 150 U.S. Army special operations troops to Jordan, partly to help monitor Syria's chemical weapons stockpile. "We want to ensure that security is maintained and we want to be very sure that those (weapons) do not fall into the wrong hands," he says.
December 3, 2012
Obama and Secretary of State Hillary Clinton repeat U.S. warnings after a U.S. official tells CNN that Syria has begun combining chemicals that can be used to produce the nerve gas sarin. White House spokesman Jay Carney says Washington is concerned that "an increasingly beleaguered regime" may be considering their use.
December 10, 2012
In a letter to U.N. Secretary-General Ban Ki-moon, Syria accuses the United States of falsely accusing it using chemical weapons: "What raises concerns about this news circulated by the media is our serious fear that some of the countries backing terrorism and terrorists might provide the armed terrorist groups with chemical weapons and claim that it was the Syrian government that used the weapons," the state-run news agency SANA reported.
December 12, 2012
U.S. officials say Syria has begun using short-range Scud missiles, which are capable of carrying both chemical and conventional weapons, against rebel targets in the country's north.
December 22, 2012
Russian Foreign Minister Sergei Lavrov says Syria has consolidated its chemical weapons into one of two locations in the face of ongoing rebel gains.
January 17, 2013
Carney says Washington has found no evidence to back up allegations that Syria used chemical weapons in a December attack on the city of Homs. Senior U.S. officials say the Syrians misused a riot-control gas in the attack, which Syrian doctors and activists said killed six people and left dozens suffering from respiratory, nerve and gastrointestinal ailments.
March 19, 2013
The Syrian government and rebel fighters accuse each other of using chemical weapons in a missile attack near Aleppo that state-run media said killed 25 people and wounded dozens more. Louay Almokdad, a spokeman for the rebel Free Syrian Army, says the attack was carried out on rebel-controlled territory and with a missile possessed only by government forces; Russia, a longtime Syrian ally, warns that weapons of mass destruction are falling into the hands of "terrorists."
March 20, 2013
-- Robert Ford, the U.S. ambassador to Syria, tells a congressional committee that there is "no evidence to substantiate" reports of a chemical attack, "but I want to underline that we're looking very carefully at these reports."
-- During a trip to Israel, Obama says his administration is trying "to find out precisely whether or not this red line was crossed." But he added, "I am deeply skeptical of any claim that, in fact, it was the opposition that used chemical weapons."