US President Donald Trump has hailed an overnight military strike on Syria as "perfectly executed", adding: "Mission Accomplished".
The US, UK and France attacked three government sites, targeting what they said were chemical weapons facilities.
More than 100 missiles struck in response to a suspected deadly chemical attack on the town of Douma last week.
Russian President Vladimir Putin said he condemned the Western strikes "in the most serious way".
Russia, whose forces are bolstering Syria's government, had threatened military retaliation if any Russian personnel had been hit.
In early morning tweets from Washington, President Trump thanked France and the UK for "their wisdom and the power of their fine military".
A perfectly executed strike last night. Thank you to France and the United Kingdom for their wisdom and the power of their fine Military. Could not have had a better result. Mission Accomplished!— Donald J. Trump (@realDonaldTrump) April 14, 2018
A Pentagon briefing on Saturday said the strikes had "set the Syrian chemical weapons programme back for years".
Later there was a bitter exchange between the US and Russia at the United Nations.
The wave of strikes is the most significant attack against President Bashar al-Assad's government by Western powers in seven years of Syria's civil war.
Responding to the strikes, Mr Assad said in comments published by his office: "This aggression will only make Syria and its people more determined to keep fighting and crushing terrorism in every inch of the country."
Where was hit?
At a Pentagon briefing on Saturday, Lt Gen Kenneth McKenzie listed the three targets that had been struck in a "precise, overwhelming and effective" manner:
- The Barzah chemical weapons research and development centre near Damascus was hit by 76 missiles, 57 of them Tomahawk cruise missiles, and "destroyed"
- The Him Shinshar chemical weapons storage facility near Homs was hit by 22 missiles - nine US Tomahawks, eight British Storm Shadows and five naval cruise missiles and two Scalp cruise missiles launched by France
- The Him Shinshar chemical weapons bunker facility near Homs was targeted with seven Scalp missiles and was "successfully hit"
Gen McKenzie said the "initial indications are that we accomplished the military objectives without interference from Syria".
He said "none of the aircraft or missiles were successfully engaged" by defence systems and all aircraft had returned.
Gen McKenzie said about 40 Syrian defence missiles were fired, mostly after the targets were hit. No Russian defence systems were operated, he said.
The Pentagon briefing conflicted with information given at a Russian defence ministry briefing, which said Russian units had tracked the actions of the US and UK forces, but not the French.
The ministry said 103 cruise missiles had been launched and 71 were shot down by Syrian systems.
It accepted the "alleged chemical weapons facilities" near Damascus and Homs were "partially destroyed".
The ministry said there were other locations that were targeted but not hit, including Damascus International Airport and the al-Dumayr and Blai airdromes, and the Shayrat air base.
The ministry said "preliminary information" suggested there had been no casualties among the Syrian army or civilians.
The Pentagon said it also had no confirmation of any civilian casualties.
The US had communicated with Russia ahead of the strikes through the normal procedures of their "deconfliction" hotline, which is used to prevent accidental clashes in a war zone.
There had been concerns that if the US strike had hit Russian military personnel on the ground, it would further escalate tension.
The US says the scale of the strikes was about "double" what was launched in April 2017 after a chemical attack on the town of Khan Sheikhoun that killed more than 80 people.
What was said at the UN?
At an emergency meeting of the UN Security Council called by Russia, the Russian envoy to the UN, Vassily Nebenzia, read out a quote from President Putin saying the action of the US and its allies had made a "catastrophic situation in Syria even worse".
Mr Putin accused the allies of "cynical disdain" in acting without waiting for the results of a chemical watchdog investigation into the Douma attack. The Organisation for the Prohibition of Chemical Weapons (OPCW) inspectors are expected to arrive in the area this weekend.
US envoy Nikki Haley said the strikes were "justified, legitimate and proportionate".
She said the US and its allies had given diplomacy "chance after chance" but Russia had continued to veto UN resolutions.
She said: "We cannot stand by and let Russia trash every international norm and allow use of chemical weapons to go unanswered."
Ms Haley said she had spoken to President Trump and he had said the US was "locked and loaded" if Syria used chemical weapons again.
She said: "When our president draws a red line, our president enforces the red line."
Bashar Jaafari, Syria's envoy to the UN, repeated that the alleged Douma attack was a "masquerade" mounted by rebels.
He also said OPCW inspectors had previously visited the targeted Barzeh site and reported no chemical weapons activities there.
UN Secretary General Antonio Guterres said he wanted to remind all members that "there is an obligation to act consistently with the charter of the UN and international law in general" and added that there was "no military solution" to the Syria crisis.
The UN Security Council rejected a Russian resolution condemning the strikes.
What role did the UK and France play?
According to the UK Ministry of Defence, four RAF Tornado jets hit a site near Homs with eight Storm Shadow cruise missiles.
Prime Minister Theresa May said there was "no practicable alternative to the use of force" but also added that the strikes were not about "regime change".
French President Emmanuel Macron also confirmed his country's participation in the operation.
"Dozens of men, women and children were massacred with chemical weapons," he said of the Douma incident a week ago.
On Saturday, the Syrian army announced that the eastern Ghouta region, where Douma is situated, had been cleared of the last rebel fighters and was fully retaken.
Analysis: Will this time be different?
Jonathan Marcus, BBC defence correspondent
This attack was more significant than the US strike against a Syrian air base a little over a year ago, but at first sight seems more limited than President Trump's rhetoric may have suggested.
Last year some 59 missiles were fired. This time a little over double that number were used.
The strikes are over for now, but there was a clear warning that if the Assad regime resorts to chemical weapons again, then further strikes may well follow.
Care was taken, say the Americans, to avoid both Syrian and "foreign" - for that read Russian - casualties.
But the fundamental questions remain. Will President Assad be deterred?
Last year's US strike failed to change his behaviour. This time, will it be any different?
How has the rest of the world responded?
German Chancellor Angela Merkel - who had ruled out joining the military action - said she supported the strikes as "necessary and appropriate".
Nato Secretary General Jens Stoltenberg said the Nato allies fully supported the actions of the US, UK and France.
Israeli PM Benjamin Netanyahu expressed his "total support" for the air strikes.
I support the actions by the US, UK and France against the #Syrian regime's chemical weapons facilities and capabilities. #NATO considers the use of chemical weapons unacceptable. Those responsible must be held accountable. https://t.co/HPQ4YpTT7Y— Jens Stoltenberg (@jensstoltenberg) April 14, 2018
China said it opposed the use of force and that there could only be a political solution to the Syrian conflict.