The team from the Organisation for the Prohibition of Chemical Weapons was delayed for several days in its attempts to reach Douma.
Chemical inspectors arrive at attack site in Syria, says Russia
A team of international chemical weapons inspectors arrived on Saturday in the Syrian town of Douma, where a chemical attack took place on April 7, Russia's foreign ministry said.
"According to information we have, the special Organisation for the Prohibition of Chemical Weapons mission... arrived on the morning of April 21 in the city of Douma at the sites suspected of having toxic substances," the ministry said in a statement.
The team from the OPCW had been waiting for days in the Syrian capital of Damascus for clearance to enter Douma. They had originally planned to head to the town on Wednesday, but that got pushed back after a risk assessment team from the United Nations came under fire on Tuesday, as it inspected the site.
Ministry spokeswoman Maria Zakharova said the delay was "unacceptable".
Russia, whose forces in Syria back President Bashar Al Assad's army, has denied claims that Syrian forces carried out the April 7 attack that prompted a retaliatory missile strike by the United States, Britain and France.
The attack in Douma, the eastern Damascus town now fully under Syrian government control after a years-long siege, is believed to have killed dozens.
Russia's announcement came as rebels began leaving three towns in the eastern Qalamoun region in the Damascus countryside, according to Syrian state media.
Al Ikhbariya TV said buses carrying hundreds of opposition fighters and their families left the towns of Al Ruhayba, Jayrud and Al Nasiriya on Saturday, on their way to rebel-held territory near the Syrian-Turkish border. As many as 3,200 rebels could leave over the course of the day, the station said, with further evacuations expected over the coming days.
The evacuations followed the striking of a new deal between opposition fighters and the Russian-backed regime, in which rebel groups agreed to surrender the enclave, state media said.
It is another victory for President Assad, who is seeking to recover control of the last few rebel-held areas near the capital following the defeat of the insurgency in eastern Ghouta.
"An agreement has been reached in the area of eastern Qalamun providing for terrorists to exit Al Ruhayba, Jayrud and Al Nasiriya,” news agency Sana said on Friday night, using its usual term for rebels.
It is the latest deal to be reached in which fighters agree to relocate with their families to north-western Syria. Tens of thousands of people have been transferred out of the areas around Damascus in recent weeks as the government reconsolidates control.
The eastern Qalamoun area is 40 kilometres from Damascus and includes several towns in an expanse of mountainous territory.
Last week, a separate deal led to hundreds of Syrian rebels in Dumayr, a town north-east of Damascus, handing in their weapons and boarding buses to leave. That departure was likely to involve 1,500 fighters from the Jaish Al Islam rebel faction with 3,500 of their family members, Sana said.
Russia has been deeply involved in the deal-striking process, negotiating with rebels and placing masked military escorts aboard buses, underscoring its larger ground-level presence across Syria.
The evacuation of eastern Qalamun leaves just two besieged rebel enclaves in Syria, one located north of Homs and one in southern Damascus where ISIS and other extremist factions are present.