The cabinet of British Prime Minister Theresa May has agreed action needs to be taken against the use of chemical weapons in Syria.
Syrian President Bashar al-Assad denies using chemical weapons against civilians in the town of Douma on Saturday.
Dozens of people were killed and hundreds injured.
The British cabinet met earlier and agreed to work with the United States and France to coordinate an international response.
In a statement released following the meeting, the British cabinet said: "The Prime Minister (Theresa May) said it was a shocking and barbaric act which killed up to 75 people, including children, in the most appalling and inhumane way.
"Cabinet agreed that the Assad regime has a track record of the use of chemical weapons and it is highly likely that the regime is responsible for Saturday's attack.
"The Prime Minister said it was a further example of the erosion of international law in relation to the use of chemical weapons, which was deeply concerning to us all.
"Following a discussion in which every member present made a contribution, cabinet agreed it was vital that the use of chemical weapons did not go unchallenged.
"Cabinet agreed on the need to take action to alleviate humanitarian distress and to deter the further use of chemical weapons by the Assad regime."
"Seriously consider" the consequences
Meanwhile Maria Zakharova, a spokeswoman for the Russian foreign ministry, said Donald Trump's threat to launch missiles at Syrian forces is a "test for each and every country (with troops in Syria) to protect its people on the ground".
Russia and Iran are the Assad regime's allies in the Syrian civil war.
The Kremlin said on Wednesday that the US and its allies - France, Germany and the UK - should "seriously consider" the consequences of their threats to launch military action in response to an alleged chemical attack carried out on Saturday in Douma, eastern Ghouta, on the outskirts of Damascus.
US President Donald Trump at the White House in Washington | Image: Chris Kleponis/DPA/PA Images
Ms Zakharova said: "Russia should protect its people on the ground, of course.
"We came to Syria at the invitation of the people. You can see their appreciation on the ground."
She refused to admit there had been a chemical attack on Douma over the weekend, claiming Russia is "100% sure that that was a clear provocation".
She claimed to have proof that the White Helmets - the Syrian volunteer organisation which mainly operates in rebel-controlled areas - were responsible.
Analytic monitoring by the Russians has proved that the White Helmets are working with terrorist organisations in Syria, she claimed.
"We'll see what happens"
Russia wants experts from the Organisation for the Prohibition of Chemical Weapons (OPCW) to go to Syria as "quickly as possible", with the Kremlin providing help, she added.
The chemical weapons watchdog has said it will deploy a fact-finding mission to Douma "shortly".
US President Donald Trump appears to have rolled back somewhat on his threat to target Syria with a missile strike.
In a tweet on Wednesday, he warned Russia to "get ready" for a missile strike and that US missiles "will be coming" in response to the alleged chemical weapons attack.
However in a tweet earlier on Thursday, Mr Trump said he "Never said when an attack on Syria would take place" - adding that it "could be very soon or not so soon at all."
Mr Trump has been meeting his National Security Council, simply tell reporters earlier: "We'll see what happens, folks - we'll see what happens".