Following an emergency meeting lasting more than two hours on Thursday, Theresa May’s top ministers agreed Britain should continue to work with the US and France on a coordinated response.
The Cabinet’s approval for action raised the likelihood of Britain joining France and the US in a military response against Syria’s government.
It also suggested the Prime Minister is set to defy calls from opposition parties for Parliament to be recalled in order for MPs to vote on authorising intervention.
Mrs May later spoke to US President Donald Trump during a telephone call, in which Number 10 said the two leaders agreed “it was vital that the use of chemical weapons did not go unchallenged, and on the need to deter the further use of chemical weapons by the Assad regime”.
A Downing Street spokesperson added: “They agreed to keep working closely together on the international response.”
The US President was also due to hold a call with French President Emmanuel Macron, with the White House having revealed Mr Trump is still yet to make a “final decision” on action.
The Cabinet agreed with the Prime Minister’s assertion it is “highly likely” President Assad’s regime carried out a “shocking and barbaric” suspected gas attack in the Syrian city of Douma on Saturday.
After the meeting, in which every minister present spoke, Downing Street also revealed the Cabinet “agreed it was vital that the use of chemical weapons did not go unchallenged”.
In addition, ministers were said to have “agreed on the need to take action to alleviate humanitarian distress and to deter the further use of chemical weapons by the Assad regime”.
Mr Macron claimed on Thursday he had “evidence” that chemical weapons were used in Douma by the Syrian government, including chlorine gas.
US media also reported American officials had obtained blood and urine samples from victims in Douma, which tested positive for mainly chlorine and some for a nerve agent.
Saturday’s suspected chemical attack killed up to 75 people, including children, and injured hundreds.
The Organisation for the Prohibition of Chemical Weapons, the international watchdog, confirmed a fact-finding team was on its way to Syria and would begin work on Saturday.
Russia, which backs President Assad’s regime, called for a meeting of the UN Security Council on Friday to discuss the possibility of US-led military action in Syria.
Moscow’s UN ambassador Vassily Nebenzia claimed the “immediate priority is to avert the danger of war” following a closed-door meeting of the UN Security Council on Thursday.
Asked if he was referring to war between the US and Russia, Mr Nebenzia added: “We cannot exclude any possibilities, unfortunately, because we saw messages that are coming from Washington. They were very bellicose.”
The risk of direct confrontation between Western nations and Russia in Syria was also raised by Maria Zakharova, spokeswoman for the Russian foreign ministry.
She told Sky News her country will protect its troops on the ground in Syria if missiles are launched by the US and its allies.
Moscow also claimed Syrian rebels had now capitulated in Douma, less than 10 miles from the capital Damascus, to leave the city under the complete control of President Assad’s forces and Russian military police.
Despite having declared on Monday he would make “major decisions” on a US response to the Douma attack within 48 hours, Mr Trump has now downplayed the prospect of immediate action.
He posted on Twitter: “Never said when an attack on Syria would take place. Could be very soon or not so soon at all!”
Later, US defence secretary James Mattis told Congress he believed there was a chemical attack in Syria but that the US was “looking for the actual evidence.”
Despite the backing of her Cabinet, Mrs May has failed to convince other MPs of the case for action.
Julian Lewis, the chair of the House of Commons’ Defence Committee, told Sky News the Prime Minister should be considering “smarter methods of warfare” such as a cyber attack, rather than missile strikes.
He branded the option in Syria as a “choice between monsters on the one hand and maniacs on the other”.
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Labour leader Jeremy Corbyn and Liberal Democrat leader Sir Vince Cable repeated their demands for a parliamentary vote on possible intervention in Syria, while the SNP called for Parliament to hold a rare Saturday sitting in order to debate action.
However, former MI6 chief Sir John Sawers told Sky News there was no need for Parliament to have a say as the decision “rests with the Prime Minister and the Cabinet”.