Joint air strikes by the US, UK and France have set back Syria’s chemical weapons capability “for years”, the US military said.
Cruise missiles were fired at three sites in response to what Theresa May called the “despicable and barbaric” attack in Douma last week that is believed to have killed up to 75 people.
Ms May said Bashar al-Assad could face even further strikes if chemical weapons are used again - and the US warned that they were "locked and loaded" if poison used again.
US President Donald Trump declared “mission accomplished” after more than 100 missiles were collectively launched in the early hours of the morning.
During telephone conversations on Saturday afternoon, Ms May, Mr Trump and Emmanuel Macron all agreed that the military strikes in Syria "had been a success".
Downing Street published a document setting out why it believes military action against the Syrian regime was legal after Jeremy Corbyn described the action as legally questionable.
The Russian embassy in the US said it had warned that such actions would "not be left without consequences", adding that insulting President Vladimir Putin was "unacceptable and inadmissible".
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Russia and Syria claimed most of the missiles, numbering about 110, were intercepted, while the Pentagon said Syrian defences had “no effect” on the operation.
Mr Assad, backed also by Iran, said on Saturday the bombings would increase his country’s resolve to “fight and crush terrorism”.
Ms May said she had authorised British forces to conduct precision strikes against Syria to help degrade its chemical weapons capability.
“This is not about intervening in a civil war. It is not about regime change,” Ms May said in a statement. “It is about a limited and targeted strike that does not further escalate tensions in the region and that does everything possible to prevent civilian casualties.”
RAF Tornado jets bombed a chemical weapons facility 15 miles outside Homs, the Ministry of Defence said.
Russia warned of “consequences” for the US-led military strikes, saying the use of missiles on suspected chemical weapons assets were an insult to Vladimir Putin.
“A pre-designed scenario is being implemented,” Russian ambassador Anatoly Antonov said in a statement. “Again, we are being threatened. We warned that such actions will not be left without consequences.”
Humanitarian volunteers were “seriously pressured” by the UK to speed up plans for a “provocation” in eastern Ghouta, Moscow’s defence ministry suggested.
Britain’s ambassador to the UN condemned the “blatant lie” as “the worst piece of fake news we’ve yet seen from the Russian propaganda machine”.
Later, a spokesman for the UK Foreign Office said: “These accusations from Moscow are just the latest in a number of ludicrous allegations from Russia, who have also said that no attack ever happened.
“This simply shows their desperation to pin the blame on anyone but their client: the [President Bashar] Assad regime
It comes as Russia and the United States traded fresh blows during the latest round of talks at the UN Security Council and amid warnings that the world is at risk of “full-blown military escalation”.
The State Department said the United States has proof at “a very high level of confidence” that the Syrian government of Mr Assad carried out the attack but is still working to identify the mix of chemicals used.
“Syria is responsible. We are all in agreement,” department spokeswoman Heather Nauert told reporters.
Additional reporting by agencies
Good morning, welcome to The Independent's live blog on the mounting tensions surrounding the crisis in Syria.
Theresa May and Donald Trump have agreed the use of chemical weapons must not go unchallenged after the prime minister won the backing of her cabinet on the need to "take action" to prevent their further use by the regime of Bashar al-Assad.
Meanwhile, Russia has been granted a request for the United Nations Security Council to meet on Friday for fresh discussions on Syria.
Cabinet agrees on need to 'take action' in SyriaTheresa May’s cabinet has agreed on the need to “take action” to deter the use of chemical weapons in Syria, ahead of an expected military strike on regime targets. Downing Street said an “international response” would be coordinated with allies France and the US, to show that the use of toxic weapons in the Middle Eastern country’s civil war would not be tolerated.
Jeremy Corbyn has accused the Government of 'waiting for instructions' from Donald Trump on what to do over Syria.
The Labour leader said: "Further UK military intervention in Syria's appalling multi-sided war risks escalating an already devastating conflict.
"The Government appears to be waiting for instructions from President Donald Trump on how to proceed. But the US administration is giving alarmingly contradictory signals.
"Even US defence secretary James Mattis has said we 'don't have evidence' and warned further military action could 'escalate out of control'."
Mr Corbyn added: "Ministers should take their proposals, such as they are, to parliament. And Britain should press for an independent UN-led investigation of last weekend's horrific chemical weapons attack so that those responsible can be held to account.
"Rather than further military action, what is urgently needed is a coordinated international drive to achieve a ceasefire and a negotiated settlement under UN auspices. The humanitarian priority must be to halt the killing on all sides.
"The need to restart genuine negotiations for peace and an inclusive political settlement of the Syrian conflict, including the withdrawal of all foreign forces, could not be more urgent. We must do everything we can, no matter how challenging, to bring that about."
Labour's shadow home secretary, Diane Abbott, told BBC Radio 4's Today programme: "It would be outrageous for the government not to bring military action in Syria to Parliament, for Parliament to have a vote. And the Tories used to think like that.
"The reason they are not doing it is they are frightened they will lose the vote."
Pressed on whether there were any circumstances in which Labour would back military action in Syria, Ms Abbott said: "What we are interested in is an end to the violence and we don't believe that further bombing, in this situation, will bring an end to the violence."
When she was asked if Russia or the US posed the greatest threat to world peace, Ms Abbott said: "It's clear that at this point Russia, its role in Syria, what we believe, beyond reasonable doubt, is its role in the poison gas attacks in Salisbury, is a greater threat to world peace than the United States."
Referring to Donald Trump's tweets, Russia's deputy prime minister said international relations should not depend on the mood of one person when he wakes up in the morning, the RIA news agency reported.
Arkady Dvorkovich said Russia was not prepared for such risks.
Hezbollah, an Iran-backed Islamist militant group, does not believe a direct US-Russia clash or wider all-out war will occur over Syria, its deputy leader said in a newspaper interview published on Friday.
Sheikh Naim Qassem told Lebanese daily al-Joumhouria: "The conditions do not point to a total war happening... unless Trump and Netanyahu completely lose their minds," referring to Donald Trump and Israel's prime minister, Benjamin Netanyahu.
West 'must avert danger of war' over Syria chemical attack, says RussiaThe Russian ambassador to the United Nations has urged the US and its allies not to take military action over the apparent chemical attack in Syria, saying the immediate priority was to “avert the danger of war”. International tensions have spiked over the attack, with Washington holding Russia partially culpable for what they believe is the use of chemical weapons on the town of Douma by the regime of Syrian President Bashar al-Assad.
Diane Abbott says it would be 'outrageous' for Theresa May not to consult Parliament on military action in SyriaDiane Abbott has said it would “outrageous” for Theresa May to pursue military action in Syria without consulting Parliament and give MPs a vote. The shadow home secretary also repeated a claim from Julian Lewis, the chairman of the defence select committee, that military action in the war-ravaged region could “end up with the RAF serving as the air arm of the jihadi extremist rebels in Syria”.
Here are the full quotes from Russia's deputy prime minister, Arkady Dvorkovich, who said international relations should not depend on the mood of one person when he wakes up in the morning, in apparent reference to President Trump.
"We cannot depend on the mood of someone on the other side of the ocean when he wakes up, on what a specific person takes into his head in the morning," Mr Dvorkovich said, according to the TASS news agency.
"We cannot take such risks."
In an early-morning tweet on Wednesday, Mr Trump warned missiles "will be coming" in response to a suspected chemical weapons attack by Syrian government forces. Russia is Syria's most important military ally in the country's civil war.
In another tweet on Thursday, Mr Trump appeared to cast doubt on at least the timing of any US-led military action. "Never said when an attack on Syria would take place. Could be very soon or not so soon at all!" it said.
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