The Organisation for the Prohibition of Chemical Weapons (OPCW) has said it is deploying a fact-finding mission to Douma, Syria.
Douma is the scene of a suspected chemical attack that reportedly killed at least 49 people and injured hundreds on Saturday.
Russia has denied the attack took place or that Moscow or the the Syrian military was involved.
President Bashar al-Assad's regime in Syria, which is backed by Russia, has also denied responsibility for the attack.
The Syrian American Medical Society described patients foaming at the mouth and warned that victims had suffered corneal burns and smelled of a "chlorine-like odour."
Unverified images posted by the White Helmets group show children being treated after a suspected chemical attack in Douma | Image via @SyriaCivilDef on Twitter
There has been no independent verification of the claims made by the White Helmets rescue service and other medical groups.
At an emergency meeting of the United Nations Security Council, US Ambassador Nikki Haley said Moscow had the "blood of Syrian children" on its hands.
Russia's envoy Vassily Nebenzia insisted there was "no chemical weapons attack."
At a meeting on Monday, US President Donald Trump said the US has "a lot of options militarily" adding that a response will be decided.
He said his administration will make "major decisions" over the next 24 to 48 hours in response to the "barbaric" and "heinous" attack.
In a statement, the OPCW said: " The OPCW Technical Secretariat has requested the Syrian Arab Republic to make the necessary arrangements for such a deployment.
"This has coincided with a request from the Syrian Arab Republic and the Russian Federation to investigate the allegations of chemical weapons use in Douma.
"The team is preparing to deploy to Syria shortly."
UN Secretary-General António Guterres | Image: UN Photo/Mark Garten
The United Nations Secretary-General António Guterres said of the alleged chemical weapons attack: "I am outraged by the continued reports of use of chemical weapons in the Syrian Arab Republic.
"I reiterate my strong condemnation of the use of chemical weapons against the civilian population.
"Any confirmed use of chemical weapons, by any party to the conflict and under any circumstances, is abhorrent and a clear violation of international law."
He added: "I reaffirm my full support for the Organisation for the Prohibition of Chemical Weapons (OPCW) and its fact-finding mission in undertaking the required investigation into these allegations.
"The fact-finding mission should be granted full access, without any restrictions or impediments to perform its activities.
"The norms against chemical weapons must be upheld.
"I appeal to the Security Council to fulfil its responsibility and find unity on this issue.
"I also encourage the council to redouble its efforts to agree on a dedicated mechanism for accountability."