Inspectors from the global chemical arms watchdog took samples in the Syrian town of Douma today after an alleged poison gas attack, the body said.
A fact-finding mission from the Organisation for the Prohibition of Chemical Weapons (OPCW) visited Douma "today to collect samples for analysis in connection with allegations of chemical weapons use on 7 April 2018".
"The OPCW will evaluate the situation and consider future steps including another possible visit to Douma," the organisation said in a statement.
The Russian foreign ministry said earlier the team had arrived in the town "at the sites suspected of having toxic substances".
"The security of the OPCW has been guaranteed not only by the Syrian side but also by the Russian command in Syria," the Russian ministry said.
France and the United States have accused Russia of obstructing access to the site, where medical relief agencies say dozens of people were killed. The OPCW mission arrived in Syria a week ago to investigate the incident.
Russia and Damascus say the alleged gas attack, which triggered western missile strikes on Syria, was fabricated.
The samples collected by the nine-strong team will be brought back to the OPCW's laboratories in Rijswijk, a suburb of the Dutch city of The Hague where the organisation has its headquarters.
They will be "dispatched for analysis to the OPCW's designated labs".
"Based on the analysis of the sample results as well other information and materials collected by the team" a report will be drawn up, the OPCW added.
Syrian rebels began withdrawing from an enclave northeast of Damascus today and will go to northern Syria, state TV and a rebel official said, in a surrender agreement that marks another victory for President Bashar al-Assad.
The withdrawal will restore state control over the eastern Qalamoun enclave, some 40km from Damascus.
Mr Assad, backed by Russia and Iran, is seeking to wipe out the last few rebel enclaves near Damascus, building on momentum from the defeat of the insurgency in eastern Ghouta, which was the last major opposition stronghold near the capital.
State TV said rebel fighters and their families would be transported from eastern Qalamoun to Idlib and Jarablus, a rebel-held territory at the border with Turkey, with 3,200 militants and their families expected to leave today.
The spokesman for one of the rebel groups in eastern Qalamoun said the insurgents had agreed to the deal after intensified Russian shelling killed six people in areas near the town of al-Ruhaiba earlier this week.