Allied missiles have struck at the heart of the Syrian chemical weapons arsenal, aiming to punish the Assad government for a suspected poison gas attack against civilians and deter the possible future use of such banned weapons.
"A perfectly executed strike," President Donald Trump tweeted on Saturday in the aftermath of his second decision in just over a year to attack Syria. "Could not have had a better result. Mission Accomplished!"
Syria's chief allies, Russia and Iran, called the use of force by the US, Britain and France a "military crime" and "act of aggression" with the potential to worsen a humanitarian crisis after years of civil war. The UN Security Council was meeting at Moscow's request.
"Good souls will not be humiliated," Syrian President Bashar al-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 one-hour barrage launched early on Saturday in Syria.
The strikes "successfully hit every target", Pentagon spokeswoman Dana White said at a briefing. The Pentagon said there were three targets: a chemical weapons research and development site in the Damascus area, a chemical weapons storage facility near Homs and a chemical weapons "bunker" a few kilometres from the second target.
By late Saturday in Washington, more than 12 hours after the attack, neither Syria nor its Russian or Iranian allies had retaliated, Pentagon officials said.
Disputing the Russian military's contention that Syrian air defence units downed 71 allied missiles, Marine Lt Gen Kenneth McKenzie, director of the Joint Staff at the Pentagon, said no US or allies missiles were stopped. He said Syria's air defences were ineffective and that many of the more than 40 surface-to-air missiles fired by the Syrians were launched after the allied attack was over. He said the US knew of no civilians killed by allied missiles.
A global chemical warfare watchdog group said its fact-finding mission would go as planned in Douma, where the apparent use of poison gas against civilians on April 7 that killed more than 40 people compelled the Western allies to launch their attack. Syria has denied the accusation.
But France's foreign minister said there was "no doubt" the Assad government was responsible, and he threatened further retaliatory strikes if chemical weapons were used again, as did Pentagon chief Jim Mattis, who said the assault was a "one-time shot" as long as chemical weapons weren't used again.
NATO representatives planned a special session to hear from US, British and French officials.
Trump said the US was prepared to sustain economic, diplomatic and military pressure on Assad until he ends what Trump called a criminal pattern of killing his own people with internationally banned chemical weapons.
Russian leader Vladimir Putin reaffirmed the Kremlin's scepticism about the allies' Douma claim, saying Russian military experts had found no trace of the attack. He criticised the US and its allies for launching the strike without waiting for international inspectors to visit the area.
But British Prime Minister Theresa May cited reports she said indicated the Syrian government used a barrel bomb - large containers packed with fuel, explosives and scraps of metal - to deliver the chemicals. "No other group" could have carried out that attack, May said, adding that the allies' use of force was "right and legal".