Obama warns Syria's Assad not to use chemical weapons A dramatic report from northern Syria shows how rebels control much of the countryside but remain locked in deadly battle with government forces who have the fire power. Some displaced civilians have taken refuge in the ruins of one of the Dead Cities of Syria, the ancient city Serjilla, abandoned around 1600 AD. NBC's John Irvine reports. By Catherine Chomiak, NBC News and wire services President Barack Obama warned Syrian President Bashar Assad Monday that the use of chemical weapons by the regime would be "totally unacceptable." "The world is watching," Obama said. "The use of chemical weapons is and would be totally unacceptable and if you make the tragic mistake of using these weapons there will be consequences and you will be held accountable," he added. U.S. officials told NBC News that the Syrian regime had ordered Syria's military chemical corp to "be prepared." The officials stressed the directive was not an order to use chemical weapons and did not come from Assad directly, but that order and a considerable increase in activity around Syria's chemical weapons sites have raised serious concerns. Syrian state television reported that the Syrian Foreign Ministry denied the country had any plans to use chemical weapons, no matter the circumstances. The U.S. officials say the fear is that Syrians are at least preparing to mix the precursor chemicals for sarin nerve gas that could be used in artillery shells - but acknowledged it's not clear that process has begun. Once the precursors are mixed, the sarin produced has a relatively short shelf life. In artillery shells, the precursors are packed separately inside the shells and "mixed" immediately before or shortly after the shells are fired. Despite Obama's warning that if Syria uses chemical weapons, "there will be consequences," U.S. military forces have not been put on alert or given warning orders to prepare for any possible military action against Syria. According to a senior U.S. official, there are "plenty of assets in the region which could respond quickly." Earlier, the State Department said the "use or proliferation of chemical weapons" in Syria is a red line for the United States and would result in the administration's taking "necessary steps or actions." "We are concerned about any move that might signal that they are somehow ready to use those chemical weapons on their own people," spokesman Mark Toner said Monday, adding that the U.S. is concerned that Assad's increasingly beleaguered regime might seek to up the ante in the 20-month-old uprising. When asked if the chemical weapon stockpiles are secure, Toner said the U.S. is monitoring them, but "it is hard to say, in Syria today, that any stockpile of weapons is secure." The U.S. is talking to the rebels fighting against the Assad regime about how they should secure chemical weapons that may come into their possession, a senior State Department official said. A senior U.S. defense official said Monday that U.S. and allied intelligence have detected Syrian movement of chemical weapons components in recent days. White House press secretary Jay Carney said "the world is watching" Assad and said he'll be held accountable for his actions. Carney declined to say what U.S. contingency plans involved. NBC's Jim Miklaszewski, Courtney Kube The Associated Press and Reuters contributed to this report.