Update 10.25pm: The United States has outlined plans for new economic sanctions against Russia for enabling the government of Bashar Assad in the ongoing crisis in Syria.
Stepping up the pressure on the Syrian president, US Ambassador to the United Nations Nikki Haley indicated the sanctions to be announced on Monday would be aimed at sending a message to Russia, which she said has blocked six attempts by the UN Security Council to make it easier to investigate the use of chemical weapons.
"Everyone is going to feel it at this point," Ms Haley said, warning of consequences for Assad's foreign allies.
"The international community will not allow chemical weapons to come back into our everyday life," she said.
"The fact he was making this more normal and that Russia was covering this up, all that has got to stop."
Ms Haley also made it clear that the United States will not be pulling troops out of Syria right away, saying US involvement there "is not done".
Ms Haley said the three US goals for accomplishing its mission are making sure chemical weapons are not used in a way that could harm US national interests; that the Islamic State group is defeated; and that there is a good vantage point to watch what Iran is doing.
"We're not going to leave until we know we've accomplished those things," she said.
Ms Haley said the joint military strike "put a heavy blow into their chemical weapons programme, setting them back years" and reiterated that if Assad uses poison gas again, "the United States is locked and loaded".
Russia has military forces, including air defences, in several areas of Syria to support Assad in his long war against anti-government rebels.
Russia and Iran called the use of force by the United States and its French and British allies a "military crime" and "act of aggression".
The UN Security Council met to debate the strikes, but rejected a Russian resolution calling for condemnation of the "aggression" by the three Western allies.
Assad denies he has used chemical weapons, and the Trump administration has yet to present hard evidence of what it says precipitated the allied missiles attack: a chlorine gas attack on civilians in Douma on April 7.
The US says it suspects that sarin gas also was used.
"Good souls will not be humiliated," Assad tweeted, while hundreds of Syrians gathered in Damascus, the capital, where they flashed victory signs and waved flags in scenes of defiance after the early morning barrage.
Update 4.25pm: Trump defends 'mission accomplished' statement after strike on Syria
Donald Trump has defended his use of the phrase "Mission Accomplished" to describe a US-led allied missile attack on Syria's chemical weapons programme.
The US president said that "it is such a great military term, it should be brought back".
In an early-morning tweet, President Trump said the strike was "perfectly carried out" and that "the only way the Fake News Media could demean was by my use of the term "Mission Accomplished".
He added that he knew the media would "seize" on the phrase, but said it should be used often.
He tweeted "Mission Accomplished" on Saturday after US, French and British planes and ships launched more than 100 missiles nearly unopposed by Syrian air defences.
While he declared success, the Pentagon said the bombing of three chemical-related facilities left enough others intact to enable the Assad government to use banned weapons against civilians if it chooses.
The Syrian raid was so perfectly carried out, with such precision, that the only way the Fake News Media could demean was by my use of the term “Mission Accomplished.” I knew they would seize on this but felt it is such a great Military term, it should be brought back. Use often!— Donald J. Trump (@realDonaldTrump) April 15, 2018
His choice of words recalled a similar claim associated with President George W Bush following the US-led invasion of Iraq.
President Bush addressed sailors on board a Navy ship in May 2003 alongside a "Mission Accomplished" banner, just weeks before it became apparent that Iraqis had organised an insurgency that tied down US forces for years.
The nighttime Syria assault was carefully limited to minimise civilian casualties and avoid direct conflict with Syria's key ally, Russia, but confusion arose over the extent to which Washington warned Moscow in advance.
The Pentagon said it gave no explicit warning. The US ambassador in Moscow, John Huntsman, said in a video, "Before we took action, the United States communicated with" Russia to "reduce the danger of any Russian or civilian casualties".
Update 2.05pm: Bashar Assad claims Syria airstrikes are based on 'lies'
Syria's President Bashar Assad has said the Western air strikes against his country were accompanied by a campaign of "lies" and misinformation at the UN.
He spoke on Sunday to a group of visiting Russian politicians, and his comments were carried by state media.
Assad and Russia deny using chemical weapons, the trigger for the strikes early on Saturday.
An alleged gas attack last weekend in the town of Douma killed more than 40 people, according to opposition activists and rescuers.
Assad told his visitors that the US, Britain and France, which carried out the strikes, had waged a campaign of "lies and misinformation" against Russia and Syria.
The UN Security Council has been paralysed in dealing with the seven-year Syrian conflict and the use of chemical weapons.
Russia, a veto-wielding permanent member, is a close ally of Assad.
10.14am: 'Where is the legal basis for this?' - Jeremy Corbyn hits out at Syria airstrikes
Jeremy Corbyn has called for a war powers act to give the British parliament more scrutiny over military action following the bombing campaign in Syria.
Appearing on BBC One's The Andrew Marr Show, the British Labour leader questioned the legal basis for the UK joining the US and France in airstrikes in response to the chemical weapons attack in Douma.
Mr Corbyn said Parliament should have been given a vote ahead of the strikes.
"I think what we need in this country is something more robust like a War Powers Act so that governments do get held to account by Parliament for what they do in our name."
The Labour leader warned of an escalation in a "proxy war" between the US and Russia.
He said chlorine has been used by "a number of parties in the conflict" in Syria as a weapon.
Mr Corbyn said that if Britain wants to "get the moral high ground around the world" it must abide by international law for taking military action.
"Where is the legal basis for this?" he said.
The US has warned it is "locked and loaded" if Syria carries out fresh attacks on its people.
Mr Corbyn said: "President Trump has a way with words, that's for sure. I hope it's just exaggeration on his part."
Asked if he would order military action in any circumstances if he was prime minister, the Labour leader replied: "No-one would ever say never."
Britain's Foreign Secretary Boris Johnson said "finally the world has said enough is enough" as he defended the "proportionate" action.
He told BBC One's The Andrew Marr Show: "There is no proposal on the table at the moment for further attacks because so far - thank heavens - the Assad regime has not been so foolish to launch another chemical weapons attack."
Mr Johnson added: "If and when such a thing were to happen then clearly, with allies, we would study what the options were."
Asked if there were any circumstances in which he would back air strikes in Syria, Mr Corbyn replied: "I can only countenance involvement in Syria if there is a UN authority behind it.
"If we could get to a process in the UN where you get to a ceasefire, you get to a political solution, you then may well get to a situation where there could be a UN force established to enforce that ceasefire.
"That surely would save a lot of lives."