The UN Security Council was set to meet at Moscow's request at 1500 GMT over the operation, which was unleashed by the US, Britain and France in response to an alleged chemical weapons attack on the rebel-held town of Douma.
The strikes were targeted to inflict maximum damage on sites linked to chemical weapons development. A top Pentagon official, Lieutenant General Kenneth McKenzie, said the action would set back Syria's chemical weapons program "for years."
The sounds of massive explosions rang out across Damascus just before dawn on Saturday, ushering in 45 minutes of explosions and the roar of warplanes, AFP's correspondent in the city said.
Flashes flared in the distance and by daybreak, plumes of smoke could be seen rising from the city's north and east.
"A perfectly executed strike last night. Thank you to France and the United Kingdom for their wisdom and the power of their fine Military," Trump tweeted early Saturday.
"Could not have had a better result. Mission Accomplished!"
Both the regime of Syria's Bashar al-Assad and its ally Russia have denied all responsibility for the deadly Douma attack, and Moscow slammed the "aggressive actions" of the Western coalition, but it has not yet responded militarily.
'Crimes of a monster'
US President Donald Trump announced the joint action against Assad's regime from the White House late Friday.
Trump said the strikes were a direct response to the April 7 attack on Douma, outside Damascus, that rescuers and monitors say killed more than 40 people.
"The evil and the despicable attack left mothers and fathers, infants and children thrashing in pain and gasping for air. These are not the actions of a man. They are crimes of a monster instead," Trump said.
US Defense Secretary Jim Mattis called the strikes a "one-time shot" with no additional military action planned for now.
The strikes were the biggest foreign military action so far against Syria's regime.
The targets included a scientific research facility near Damascus, a chemical weapons storage facility west of the city of Homs, and a third location near Homs that contained both a command post and a chemical weapons equipment storage facility, the US military said.
The facilities hit had however reportedly been evacuated in recent days.
Syrian state media reported only three people injured, while Russia's defense ministry said there were "no victims" among Syrian civilians and military personnel.
Assad, who has denied ever using chemical weapons against his opponents, responded to the strikes with a defiant vow.
"This aggression will only make Syria and its people more determined to keep fighting and crushing terrorism in every inch of the country," he said.
Assad's key ally Iran also slammed the attack, with supreme leader Ayatollah Ali Khamenei describing Western leaders as "criminals."
The Russian military claimed Syrian air defense systems had intercepted 71 Western missiles, though the Pentagon disputed that.
Rally in Damascus
In central Damascus, dozens of Syrians arrived on bicycles, on foot and in cars spray painted with the red, white, and black colors of the Syrian flag, blaring patriotic tunes.
Nedher Hammoud, 48, claimed to have seen missiles "being shot down like flies."
"Let them do what they want, kill who they want... History will record that Syria shot down missiles -- and not just missiles. It shot down American arrogance."
Despite the strikes, the Organisation for the Prohibition of Chemical Weapons said it was still planning on carrying out its investigation into the Douma attack.
Thousands of rebels and civilians have since been bussed out of the town under a Russian-brokered deal. Syrian internal security forces entered Douma on Saturday and were poised to declare their control over it within "hours."
Jaish al-Islam, the group that held Douma, said it only abandoned the town because of the chemical attack.
Leading Jaish al-Islam member Mohammad Alloush said Saturday the Western strikes had not gone far enough.
"Punishing the instrument of the crime while keeping the criminal -- a farce," Alloush wrote on Twitter.
And Ahmad, a 25-year-old mechanic who had been displaced from Douma, told AFP the Western strikes were too little, too late.
"Assad won't collapse. They'll bomb for a day or two and then the regime will take it out on us," he said.
The specter of military strikes had hung over Syria since harrowing footage of victims in Douma sparked outrage from Trump, French President Emmanuel Macron and British Prime Minister Theresa May.
France said it fired cruise missiles from frigates in the Mediterranean and deployed fighter jets from home bases on Saturday.
Britain's defense ministry said four British Tornado jets had fired Storm Shadow missiles at a base 15 miles (25 kilometers) west of Homs.
UN chief urges restraint
The Russian military had vowed to respond to any attack, and President Vladimir Putin's administration had repeatedly warned Trump was taking America down a dangerous path.
Despite the warnings, Washington, Paris and London insisted their own secret intelligence belied Assad's guilt. A US spokeswoman said Friday the allies had "proof."
UN Secretary General Antonio Guterres, who delayed a planned trip to Saudi Arabia and was to brief the Security Council, called for calm.
"I urge all member states to show restraint in these dangerous circumstances," he said in a statement.