There are growing concerns that Syrian President Bashar Assad could resort to the use of chemical weapons in the country's civil conflict. Both the UN and the US have issued fresh warnings against their use.
The latest warnings came from US Defense Secretary Leon Panetta and United Nations Secretary-General Ban Ki-moon on Thursday.
"I think there is no question that we remain very concerned, very concerned that as the opposition advances - in particular on Damascus - that the regime might very well consider the use of chemical weapons," Panetta told reporters in Washington. "The intelligence that we have raises serious concerns that this is being considered."
When asked by reporters how the US would respond of Assad did use chemical weapons, the defence secretary refused to be specific.
"I'm not going to speculate or comment on what those potential consequences would be," Panetta said. "But I think it's fair enough to say that their use of those weapons would cross a red line for us."
Earlier in the day, UN Secretary-General Ban Ki-moon expressed his concerns to the head of the Organization for the Prohibition of Chemical Weapons (OPCW), Ahmet Uzumcu.
A UN press officer told the Reuters news agency that the secretary-general used a telephone conversation with Uzumcu to inform him of the contents of a letter he had written to Assad.
"The Secretary-General informed (Uzumcu) that he has written again to President al-Assad urging him to refrain from the use of any such weapons under any circumstances and underscoring the fundamental responsibility of the Syrian government to ensure the safety and security of any such stockpiles," the press officer said.
According to the OPCW, Syria is just one of six countries that have neither signed nor acceded to the Chemical Weapons Convention aimed at ending their use.
A statement posted on the OPCW's website said that it would continue to monitor developments in Syria with regard to concerns about chemical weapons.
Meanwhile, the International Committee of the Red Cross (ICRC) has said that it is carrying out "contingency planning" to protect its almost 100 aid workers in Syria in the event that chemical weapons are used. However, the ICRC's deputy head of operations, Regis Savioz told reporters in Geneva that even in such an event, Red Cross workers would continue to do "whatever we can in the circumstances to respond to the needs and keep trying to deliver our operation as we do today."
The Assad regime has denied any plans to use chemical weapons.
"Even if such weapons existed in Syria, they would not be used against the Syrian people," Syrian Deputy Foreign Minister Faisal al-Mokdad said in an interview with Lebanese television station Al Manar.
pfd/mz (Reuters, dpa, AP)