The attack, which killed more than 40 people, has drawn worldwide outrage and prompted the United States and its allies to consider a military strike on Syria, something Moscow has strongly warned against. Russian Federation says the United Nations ordered the visit stopped for security reasons, and Syrian officials say they've been meeting with the OPCW delegation.
Syrian air defenses responded firmly to the Western powers' attacks, shooting down most of the missiles fired at the country.
The US and France say they have evidence that poison gas was used in the 7 April attack in the opposition-held town of Douma, killing dozens of people, and that Syrian President Bashar Assad's military was behind it.
The four nations confronted each other intense emergency talks at the Organisation for the Prohibition of Chemical Weapons (OPCW) in The Hague as inspectors prepare for a hard and risky mission. There's no evidence of tampering of any kind.
"They will go directly to any sort of companies that were dealing with equipment related to Assad and chemical-weapons use", Haley said.
It also slammed the United States, saying the weekend strikes on three facilities in Syria were a bid "to undermine the credibility" of the mission.
The US envoy to the OPCW has expressed concern that Russian Federation had visited the site and "may have tampered with it" to impede the investigation - an allegation Russian Federation has rejected.
Syrian state media made no mention of the strike on Dumair.
It included a visit to the main hospital to which the victims of the alleged chemical attack where taken.
Hours after the attack was reported, the rebels controlling Douma agreed to withdraw.
Despite a US-Russian agreement to completely eliminate Syria's chemical weapons program after hundreds of people were gassed with sarin in Ghouta on August 21, 2013, the OPCW had been unable to verify that all manufacturing, storage and research facilities were destroyed.
At least 40 people were killed in the Douma attack.
The OPCW received the Nobel Peace Prize for its efforts to eliminate chemical weapons in 2013 as it pressed a campaign that resulted the following year in the destruction of Syria's declared stockpiles.
Russian ambassador Shulgin repeated the accusations telling reporters in The Hague that Douma residents had not been able to produce "a single body".