Russian Federation and Syria had cited "pending security issues to be worked out" while inspectors from the Organisation for the Prohibition of Chemical Weapons were denied access to the site of the alleged attack, said Ahmet Uzumcu, the director general of the OPCW.
Chemical weapons inspectors in Syria are to be given access to an alleged chemical attack site on Wednesday, Russia said.
The team's entry into Douma came 10 days after the alleged attack, raising concerns that any evidence the inspectors find could be useless.
In fact, Russian Federation informed the OPCW that "there were still pending security issues to be worked out before any deployment could take place", Ahmet Uzumcu, the director general of the OPCW technical secretariat, said in a statement on Monday.
"Or maybe they are afraid that the experts, after conducting their work on the ground, will refute the false version which served as a reason for the air strike carried out by the United States, Britain and France against defenceless Syria".
Journalists in Damascus were prevented by government minders from contacting the OPCW inspectors, and The Hague-based organization refused to comment on "operational details regarding the Douma deployment".
Assad has repeatedly denied using chemical weapons.
British Prime Minister Theresa May accused the Syrian government and its ally Russian Federation of trying to cover up evidence and obstruct the investigation.
At least 40 people are believed to have been killed in the 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. On Saturday, the U.S., France and Britain bombarded sites they said were linked to Syria's chemical weapons program.
It was the first time MPs had the chance to question Mrs May over her decision to join the USA and France in attacking Syria due to the Easter break.
The Associated Press, during a government-organized visit Monday to Douma, spoke to survivors and witnesses who described being hit by gas.
He denied that Russian Federation was hampering the mission and suggested the approval was held up because of the Western air strikes. Trump was also willing to meet Russian President Vladimir Putin, she added, while indicating that no such encounter was imminent.
"Do we sit back, do we defend (human) rights by saying, 'Rights are for us, principles are for us, and realities are for others?' No, no!" the French leader said.
"At the end of the day, we are not expecting any retaliation because the U.S. and its allies already carried out retaliatory strikes", she said. On Tuesday, Kirillov said that inspectors would be allowed once the roads leading to the site were "cleared of mines" and tested by United Nations forces for safety, according to NPR News. A Pentagon spokeswoman said there was no USA military activity in the area. He said the Obama administration did not agree to such an offer.
The latest round of diplomatic maneuvering comes as US-backed Kurdish forces fighting the Islamic State group face a Turkish assault in northern Syria. Saudi Arabia is also a member of the US -led coalition battling IS militants.
In the wake of the furious row over the poisoning of former double agent Sergei Skripal and his daughter, Yulia, in Salisbury, Russian foreign minister Sergey Lavrov said East-West relations were now worse than they were at the time of the Cold War.
"As with any crime scene, it is crucial to get there as soon as possible", said Olivier Lepick, a fellow at the Paris-based Foundation for Scientific Research.
She told MPs in the House of Commons that there was "clear evidence" the Bashar al-Assad government was behind a recent chemical weapons attack in Douma and it had been necessary to go ahead with the action without recalling Parliament for a vote on the issue to maintain the "vital security" of the military operation. Israel did not confirmed or deny mounting the raid.