Russian Federation has warned the West against attacking its Syrian ally President Bashar al-Assad, who is also supported by Iran, and says there is no evidence of a chemical attack in Douma, a town near Damascus which had been rebel-held until this month.
They agreed that the use of chemical weapons must not "go unchallenged".
A separate YouGov survey on Thursday found 61 percent of people think it would be necessary for parliament to vote on military action against Syria, with just 18 percent saying it was not necessary and 21 percent undecided.
He said Britain had told the White Helmets, who act as first responders in rebel-held areas, to fake the suspected chemical attack in the town of Douma.
Syria Attack 'Very Soon Or Not So Soon At All!'
But the Kremlin itself has avoided repeating the shoot-down warning, when asked repeatedly about it Wednesday . But the action Mr Trump threatened would probably be aimed at military targets such as Mr Assad's airbases.
British and French foreign ministers have condemned the use of chemical weapons by anyone and anywhere, a Foreign and Commonwealth Office statement said Monday.
"They agreed to keep working closely together on the worldwide response", the statement concluded.
"Six in ten Brits (61%) say that it should be necessary for Parliament to vote first on whether the United Kingdom takes part in military action in Syria - 18% say it should not be necessary for Parliament to vote on the matter", the pollster wrote on Twitter on the results of its survey.
Syria's been fighting civil war for over seven years.
Britain's Prime Minister is deciding whether to get involved in military action in Syria.
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British lawmakers voted down taking military action against Damascus in 2013, in what was widely viewed as an assertion of parliamentary sovereignty on the use of force.
Corbyn has said any action in Syria should be put to a parliamentary vote. Downing Street spokesmen repeatedly declined to comment on that report.
The latest events in Douma are examples of the Assad regime's "violation of worldwide norms", British Prime Minister Theresa May said Monday.
Some members of May's Conservative party have urged caution of intervening in a highly complex situation with many different players. "All the indications are that the Syrian regime was responsible".
Russia calls on West to think twice before launching strikes on Syria
Syria and its ally, Russia, deny any such attack, which activists say killed more than 43 people last weekend. Aid groups have blamed the Assad regime , backed by Russian Federation and Iran.