The United Nations is withdrawing "all non-essential international staff" from Syria because of security concerns, it announced on Monday.
In an online statement, the U.N. Office for the Coordination of Humanitarian Affairs (OCHA), said: "The U.N. has decided to send all non-essential international staff out of Syria and to halt all field trips outside of the capital for now."
It is expected that up to 25 of around 100 foreign workers could leave this week.
Syria's capital, Damascus, had been considered safe until last week when the main airport was shutdown after rebel attacks, the OCHA explained.
Sabir Mughal, the U.N's chief security advisor in Syria, said: "There is an increased risk for humanitarians as a result of indiscriminate shooting or clashes between the parties."
News of the U.N's decision coincided with confirmed reports from American defense officials of activity at the regime's known chemical sites, including movements of weapons.
On Monday evening AFP quoted an unnamed US official who claimed the regime has already begun mixing chemicals that can be used to make deadly sarin gas.
"We've picked up several indications which lead us to believe that they're combining chemical precursors," the anonymous source is reported to have said.