Journalists in Damascus were prevented by government minders from contacting the OPCW inspectors, and The Hague-based organisation refused to comment on "operational details regarding the Douma deployment".
The AP visited a two-room underground shelter where Khaled Mahmoud Nuseir said 47 people were killed, including his pregnant wife and two daughters, 18-month-old Qamar and 2 1/2-year-old Nour.
Syria's United Nations ambassador Bashar Jaafari told the Security Council on Tuesday that the OPCW experts would begin their investigation once they received the all-clear from the security team.
The Syrian army began preparatory shelling for an assault on the last area outside its control near Damascus on Tuesday, a commander in the pro-government alliance said, building on its recent capture of the major suburb of eastern Ghouta.
Russian Foreign Ministry spokeswoman Maria Zakharova dismissed allegations that Russia was trying to hamper the OPCW inspectors, saying Moscow strongly supports their mission to Douma.
The US ambassador to the OPCW, Ken Ward, had claimed Monday that the Russians had already visited the site and "may have tampered with it".
Survivors reached by the Associated Press said they were overwhelmed by the smell of chlorine on the night of April 7.
FRENCH president Emmanuel Macron faced protests over the Syria bombing raid as he visited the European Parliament.
"Three countries have intervened, and let me be quite frank, quite honest - this is for the honor of the global community", he said in the French city of Strasbourg.
"As it is, even with this latest bombing, the West does not have a seat at the table", said the former USA diplomat, now a fellow at the Atlantic Council think-tank.
The missiles targeted Shayrat air base, it said - but did not say who fired the missiles.