UN inspectors are due to begin a second day of investigation into last week's alleged chemical-weapons attack in the suburbs of the Syrian capital, Damascus.
They are expected to visit the four sites of suspected poison-gas attacks on Tuesday or Wednesday.
The Syrian opposition says more than 1,300 people died when toxic gases were unleashed on Eastern Ghouta and Moadamiya - two neighborhoods on the outskirts of Damascus - last Wednesday.
The UN team came under sniper fire on Monday as they tried to visit an area in western Damascus.
The convoy of six vehicles was shot in the buffer zone between rebel and government areas near Damascus as it travelled to Moadamiya and Ghouta.
Martin Nesirky, UN spokesman, told Al Jazeera the convoy had managed to reach Moadamiya, and also visited two field hospitals to take samples and interview victims.
"They are technical and medical specialists. Their aim is to collect blood and soil samples. They can also collect witness testimony. They will then analyse the samples, along with evidence, to determine what happened," he said.
However, he said the inspectors' mandate was only to determine whether chemical agents were used, not who used them.
The alleged chemical-weapons attack killed 355 people and injured thousands, according to the aid group Medecins Sans Frontieres.
Western powers blame the Syrian regime and say that potential evidence in the area has probably been destroyed by heavy government shelling over the past five days.
The Syrian government has described the allegations as "illogical and fabricated".