The Cabinet said it was "highly likely" Syria's government was behind a suspected chemical attack on a rebel-held Syrian town that killed as many as 75 people.
Theresa May's government has called on the world to "take action" against the Syrian government over a suspected chemical weapons attack — clearing the path for the UK to join the US and its allies in military action.
May's Cabinet agreed it was "highly likely" that Syrian President Bashar Assad's forces were behind the attack against a rebel-held town that has left as many as 75 people dead.
The prime minister later spoke with President Donald Trump on the phone and agreed with him that Assad could "not go unchallenged."
May's Cabinet met for over two hours in Downing Street before coming to a final agreement. A Downing Street source told Business Insider the Cabinet was "unanimous" in the need for action, with Foreign Secretary Boris Johnson making a passionate case for an intervention.
A representative said the Cabinet had agreed "on the need to take action to alleviate humanitarian distress and to deter the further use of chemical weapons by the Assad regime" and that "the prime minister should continue to work with allies in the United States and France to coordinate an international response."
The agreement means Britain could take part in strikes against Syria within days, potentially without a vote in Parliament.
The biggest US task force since the Iraq War is on course for the region.
The US is assembling 10 warships and two submarines in the Mediterranean and Gulf region, giving Trump and his allies the option for a more extended campaign against Assad.
The timing of any attack, however, remains in doubt. On Thursday, Trump rowed back from his earlier suggestions an attack was imminent, tweeting that any strikes "could be very soon or not so soon at all!"
The US defense secretary, James Mattis, also indicated that the US was still considering its options, telling the House Armed Services Committee the administration's main concern about a military response was to keep the Syria conflict from "escalating out of control."
Any military action by May would be highly divisive in both the UK Parliament and among the UK public.
One opinion poll released Monday found that just one in five members of the public supported an attack.
The YouGov poll found that 22% of Brits supported military action in Syria, while 43% opposed it.
The Labour leader Jeremy Corbyn on Friday all but ruled out backing UK military action against Syria, saying "more bombing, more killing, more war will not save life" in Syria.
Corbyn warned that any attack could trigger a wider conflict with Russia.
"The dangers of bombing now, which could escalate the conflict beyond belief … Just imagine the scenario if an American missile shoots down a Russian plane or vice versa," he said. "Where do we go from there?"
He added that he was "not in favor of increasing military action in Syria; what I'm in favor of is a political process to bring about peace."
"This afternoon Cabinet met and received an update on the attack against innocent civilians in Douma, Syria, on Saturday.
"The Prime Minister 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.
"Cabinet agreed the Prime Minister should continue to work with allies in the United States and France to coordinate an international response."