The team of arms experts arrived in the Eastern Ghouta area on the northeastern outskirts of Damascus on Wednesday.
The inspectors braved sniper fire when they initially tried to enter Eastern Ghouta on Monday, with bullets hitting their tyres and the front window of the lead vehicle, the United Nations said.
Later that day, they were able to enter Moadamiyet al-Sham southwest of Damascus to collect evidence of the other main area allegedly hit by chemical weapons on August 21.
But they were unable to return to Eastern Ghouta as planned on Tuesday because their safety could not be guaranteed.
The 13 UN inspectors arrived in Syria on August 18 to start an investigation into whether chemical weapons have been used in the 29-month old conflict.
Before the release of UN verified report, the US and its allies have already blamed the President Assad government for the use of the banned arms and are now considering military strikes in retaliation.
However, Syrian Prime Minister Wael al-Halqi said on Wednesday that the West is seeking to turn Syria into a second Iraq and that the issue of chemical weapons use is only a pretext for war.
NJF/NJF