UN experts have returned from a visit to the site of a second alleged chemical attack near Syria's capital, a day after suspending work over safety fears.
Rebels who control the area said the inspectors had travelled in a six-vehicle convoy to the outlying Damascus suburb of Eastern Ghouta yesterday, one of the areas hit in last week's suspected attacks.
They visited Eastern Ghouta, to the northeast of the capital, under the protection of rebel fighters, said the Syrian Revolution General Commission activist group.
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 managed 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 and seven translators and backup staff arrived in Syria on August 18 to start an investigation into whether chemical weapons have been used in the 29-month old conflict that has left more than 100,000 dead.
UN Secretary General Ban Ki-moon said on Wednesday that UN inspectors needed four days in total to conclude their probe into chemical weapons use in Syria.
The team's findings would then be analysed and the result sent to the UN Security Council for "any action they would deem to take".
UN spokesman Martin Nesirky said Ban was referring to a total of four working days, suggesting the inspectors needed at least until Friday to complete their mission.
Ban's comments came as the United States and its allies were building their case for military action against the Syrian regime over the alleged chemical weapons attacks.
Opponents of President Bashar al-Assad's regime say more than 1300 people, including children, died when his forces unleashed toxic gases on Eastern Ghouta and Moadamiyet al-Sham on August 21.
The regime strongly denies the claim.