Syria on Wednesday called on the UN secretary general to set up an "independent" investigation into its claims that opposition rebels have used chemical weapons in an attack, its UN envoy said.
Western diplomats said, though, that there was no confirmation that chemical weapons had been used by either side in the two-year-old conflict.
President Bashar al-Assad's government says chemical arms were used Tuesday in the town of Khan al-Assal near the conflict hotspot of Aleppo.
Syria's UN envoy said he had delivered a letter which "requested the secretary general of the United Nations to form a specialised, independent and neutral technical mission to investigate the use by the terrorist groups operating in Syria of chemical weapons yesterday against civilians" in Khan al-Assal.
The Syrian opposition has accused government forces of using chemical weapons and also demanded an independent investigation.
UN Security Council nations are remaining cautious about the claims.
"We simply don't have any information to corroborate, verify, substantiate" the allegations by either side, a senior UN diplomat said.