Syria's state news agency says inspectors from the Organisation for the Prohibition of Chemical Weapons have reached the town of Douma to investigate reports of a suspected April 7 gas attack.
The inspectors entered Douma on Tuesday after arriving in Syria on Saturday.
The United States, Britain, and France say the Syrian government was behind the attack, and launched a wave of missiles targeting Syrian military installations on Saturday as punishment.
Syria and its ally Russia deny any chemical attack took place, and Russian officials have gone even further, accusing Britain of staging a "fake" chemical attack.
Douma was the last town held by rebels in the eastern Ghouta region outside Damascus, until they surrendered the day after the alleged gas attack.