The United Nations has confirmed that is to withdraw all "non-essential international staff" as a result of the deteriorating security situation.
The organisation said that 25 of 100 foreign staff could leave this week because humanitarian aid convoys were becoming caught in the crossfire between the Syrian government and rebel forces.
Two members of staff needed hospital treatment after being caught in the fighting near the main airport in Damascus.
The UN said that eight of their staff have been killed since the conflict began, in addition to 18 volunteers with the Syrian Arab Red Crescent.
– Radhouane Nouicer, the regional humanitarian coordinator in Syria
The security situation has become extremely difficult, including in Damascus. For as long as international humanitarian law is not fully observed by all parties to this conflict and for as long as the safety of humanitarian workers is not strictly secured, UN agencies have to review the size of their presence in the country as well as the way they deliver humanitarian aid.
Reuters is reporting that the UN is removing all "non essential international staff" out of Syria. This suspends aid missions outside the city of Damascus.
Turkey scrambled fighter jets along its border with Syria this morning, in response to the Syrian bombing of Ras al-Ain over the weekend and today.
Opposition activists say at least 12 people were killed by the bombing by Syrian forces, according to activists.
Security sources said Turkish F-16 jets were scrambled from their base in the south eastern city of Diyarbakir after the air raids on the rebel Free Syrian Army's headquarters in Ras al-Ain, in a warning to Damascus not to breach Turkish territory.
Syria would not use chemical weapons, if it had them, against its own people, the foreign ministry said in a statement on state television.
"In response to the statements of the American secretary of state, who warned Syria against using chemical weapons, Syria has stressed repeatedly that it will not use these types of weapons, if they were available, under any circumstances against its people," the statement said.
Speaking in Prague, the US Secretary of State Hillary Clinton reiterated President Obama's declaration that Syrian action on chemical weapons was a "red line" for the administration and would prompt action. She said:
"We have made our views very clear: This is a red line for the United States."
"I'm not going to telegraph in any specifics what we would do in the event of credible evidence that the Assad regime has resorted to using chemical weapons against their own people. But suffice it to say, we are certainly planning to take action if that eventuality were to occur."
Syria resumed an aerial attack on the rebel-held town of Ras al-Ayn this morning, on the border with Turkey, according to Turkish officials.
Ambulances rushed to the scene and brought at least 11 wounded the hospital in Ceylanpinar.
The attacks came a day after Syrian warplanes and artillery blasted parts of the capital Damascus and its rebellious suburbs part of what activists described as intense fighting as rebels try to push their way into the center of President Bashar Assad's power base.
President Assad was warned he would be "held accountable" if his forces use chemical weapons against rebel fighters in Syria, The New York Times reported.
The warning, from the US and European officials, came after reports the Syria military was moving weapons over the weekend. In July President Obama warned that any evidence that Assad was moving weapons in a threatening way is a "red line" that could prompt American intervention.
The Pentagon estimates that intervention to neutralise chemical weapons would require upward of 75,000 troops, according to The New York Times. An US official told the newspaper:
The president has made it clear that the use of chemical weapons in Syria would cross a red line for the United States. The Assad regime must know that the world is watching, and that they will be held accountable by the United States and the international community if they use chemical weapons or fail to meet their obligations to secure them.