A team of UN inspectors left their Damascus hotel in a convoy Saturday after completing their probe into the regime's alleged use of chemical weapons.
The 13 inspectors, led by Ake Sellstrom, loaded their luggage into seven UN vehicles before setting off from their hotel.
The team have been investigating allegations of the Syrian regime's use of chemical weapons against its own people.
The UN experts' departure heightened expectations of a possible international military strike against the regime.
US President Barack Obama said Friday the United States was weighing "limited, narrow" action against Syria, insisting the world had a duty to act after hundreds of women and children were gassed to death.
Obama emphasised he had made no "final decision" on unleashing military strikes against the Assad regime, but gave his clearest indication yet that an attack was imminent.
French President Francois Hollande said a military strike on Syria could come by Wednesday and that Britain's surprise rejection of armed intervention would not affect his government's stand.
"France wants firm and proportionate action against the Damascus regime," he said in an interview with Le Monde daily. The French parliament is due to meet Wednesday for an emergency Syria session.
Washington said that 1,429 people, including 426 children, had died in a chemical attack launched by Bashar al-Assad's regime last week.
Angela Kane, the UN disarmament envoy who had visited Syria with the UN experts, left Damascus by car on Friday to the border with Lebanon.
She is expected to brief UN Secretary-General Bank Ki-moon in New York later Saturday.
The UN experts will "expedite" a report on whether chemical weapons have been used in Syria's civil war, UN spokesman Martin Nesirky said.
Ban is ready to brief the UN Security Council on the investigation into the suspected chemical weapons attack this weekend if needed, the spokesman told a briefing in New York.
The UN chief detailed progress made by the inspection team during a meeting with UN ambassadors from Britain, China, France, Russia and the United States.
"The team has completed its collection of samples and evidence," Nesirky told reporters.
The UN experts had been tasked with taking samples from the site of the alleged attack at Ghouta, near Damascus, to laboratories in Europe.
"Dr Sellstrom's team is doing its utmost to expedite the process of analysis," Nesirky said while stressing "the need for rigorous attention to maintain the integrity of the process."
The spokesman said that the eventual report written by the inspection team would be given to all UN member states.