The new data will bolster claims by the US, Britain and other Western powers that Assad’s government still possesses and uses banned munitions.
Russia vetoed on Friday a Japanese-drafted UN Security Council resolution to extend the inquiry by one month.
A resolution needs nine votes in favour and no vetoes by the US, France, Russia, Britain or China to be adopted.
The mandate for the joint inquiry by the UN and the Organization for the Prohibition of Chemical Weapons, which has found the Syrian government used the banned nerve agent sarin in an April 4 attack, expires on Friday.
Russia vetoed an initial US bid to renew the joint inquiry by the UN and the Organization for the Prohibition of Chemical Weapons on October 24, saying it wanted to wait for the release of the investigation’s report two days later.
Russia cast a veto at the UNSC, preventing the renewal of a mandate for a mission by the United Nations and the Organization for the Prohibition of Chemical Weapons.
The March 30 air strike in the northern Syrian town of Latamneh injured around 70 people who suffered nausea, foaming at the mouth and muscle spasms.
The Syrian government rejected report by international chemical weapons watchdog that said the banned nerve agent sarin was used in April attack.
Western countries blamed Syrian armed forces for the recent gas attack in the town of Khan Sheikhoun in a rebel-held area of Idliib.
At stake is the eventual legal status of weapons that are activated without direct human intervention.