Update 9.55pm: Hundreds of Syrians took to the streets of the capital in a show of defiance following joint air strikes by the United States, France and Britain hailed by President Donald Trump as "Mission Accomplished".
Just hours earlier, Damascus was rocked by loud explosions and the sky turned bright orange as Syrian air defence units fired surface-to-air missiles in response to three waves of military strikes meant to punish President Bashar Assad for his alleged use of chemical weapons.
"A perfectly executed strike," Mr Trump tweeted after warplanes and ships launched more than 100 missiles.
Russia and Iran called the use of force a "military crime" and "hooliganism".
The UN Security Council met in emergency session to debate the strikes, but rejected a Russian resolution calling for condemnation of the "aggression" by the three Western allies.
Mr Trump's UN ambassador, Nikki Haley, told the session that the president has made it clear that if Assad uses poison gas again, "the United States is locked and loaded".
The Syrian president 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.
As the airstrikes began, Assad tweeted: "Good souls will not be humiliated."
Immediately after the attack, hundreds of residents began gathering in the landmark Omayyad square of the Syrian capital.
The strikes "successfully hit every target," US officials said - the Barzah chemical weapons research and development site in the Damascus area, a chemical weapons storage facility near Homs and a chemical weapons "bunker" a few miles from the second target.
Neither Syria nor its Russian or Iranian allies retaliated, Pentagon officials said.
The US-led operation won broad Western support. The Nato alliance gave its full backing; Secretary-General Jens Stoltenberg said in Brussels that the attack was about ensuring that chemical weapons cannot be used with impunity.
German Chancellor Angela Merkel called the attack "necessary and appropriate."
Pentagon officials said the action "took out the heart" of Assad's chemical weapons arsenal.
A former officer in Syria's chemical program, Adulsalam Abdulrazek, said the strikes hit "parts of but not the heart" of the program and were unlikely to curb the government's ability to produce or launch new attacks.
A global chemical warfare watchdog group, the Organisation for the Prohibition of Chemical Weapons, said its fact-finding mission would go as planned in Douma.
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 complete their visit to the area.
But British Prime Minister Theresa May said there was little doubt the Syrian government used a barrel bomb - large containers packed with fuel, explosives and scraps of metal - to deliver the chemicals at Douma.
"No other group" could have carried out that attack, Mrs May said, adding that the allies' use of force was "right and legal".
The attack began at 4am local time (0100 GMT) with missiles hitting the eastern suburbs of Damascus, shaking the ground from a distance.
Syrian TV called the attacks a "blatant violation of international law and shows contempt for international legitimacy".
The decision to strike, after days of deliberations, marked Mr Trump's second order to attack Syria; he authorised a barrage of Tomahawk cruise missiles to hit a single Syrian airfield in April 2017 in retaliation for Assad's use of sarin gas against civilians.
The strikes appear to signal Mr Trump's willingness to draw the United States more deeply into the Syrian conflict.
The participation of British and French forces enables him to assert a wider international commitment against the use of chemical weapons, but the multi-pronged attack carries the risk of Russian retaliation.
In his nationwide address, the president stressed that he has no interest in a lengthy fight with Syria.
"America does not seek an indefinite presence in Syria under no circumstances," he said. "As other nations step up their contributions, we look forward to the day when we can bring our warriors home."
A US-led coalition has been carrying out air strikes in Syria since September 2014 as part of a largely successful effort to break the IS grip on both Syria and Iraq.
Update 8pm: UN Council rejects Russia resolution condemning Syria airstrikes
The UN Security Council has rejected a resolution tabled by Russia calling for condemnation of the "aggression" by the United States and its allies against Syria.
Only three countries - Russia, China and Bolivia - voted in favour of the resolution at the end of an emergency meeting of the 15-member council called by Russia on Saturday. Eight countries voted against and three abstained.
A resolution needs at least nine "yes" votes to be approved.
The vote reflected the deep divisions in the UN's most powerful body, which has been paralysed in dealing with the seven-year Syrian conflict and chemical weapons use in the country.
The US, Britain and France say they launched airstrikes against Syrian chemical sites after obtaining "proof" that poisonous gas was used last weekend in Douma, killing 41 civilians.
Russia and Syria claim the attack was fabricated.
Russia's UN Ambassador Vassily Nebenzia told the UN meeting in New York that the US and its allies struck without waiting for an investigation by the Organisation for the Prohibition of Chemical Weapons, branding the attack "hooliganism".
But the US ambassador to the UN said President Donald Trump told her if the Syrian regime uses poisonous gas again, "the United States is locked and loaded" to strike again.
Nikki Haley said: "When our president draws a red line, our president enforces the red line."
She said the message from airstrikes that "crippled Syria's chemical weapons program" was "crystal clear".
"The United States of America will not allow the Assad regime to continue using chemical weapons."
She accused Russia of defending Syrian President Bashar Assad and failing to ensure that Syria's chemical weapons were destroyed as the Assad regime had pledged in 2013.