Syrian activists have claimed on numerous occasions that government forces have used chemical weapons to attack rebel fighters and civilians. The government has denied all of these allegations, describing them as mere propaganda from the opposition.
There have been a lesser number of reverse claims, as well. In July, Russia accused the rebels of deploying sarin gas near the northern city of Aleppo.
A team of United Nations chemical weapons experts arrived in Syria on August 18, after months of negotiations with the government in Damascus. The team plans to visit Khan al-Assal, where the regime and rebels accused each other of using chemical weapons in April, as well as two other still-undisclosed sites.
The map shows sites where the opposition claim government forces used chemical weapons.