The US, UK and France have joined forces to attack Syria in what they say is a targeted response to a chemical weapons attack last week.
US, British and French forces have struck Syria with more than 100 missiles in the first co-ordinated Western strikes against the Damascus government, targetting what they called chemical weapons sites in retaliation for a poison gas attack.
US President Donald Trump announced the military action from the White House on Saturday, saying the three allies had "marshalled their righteous power against barbarism and brutality".
As he spoke, explosions rocked Damascus.
The bombing represents a major escalation in the West's confrontation with Assad's superpower ally Russia, but is unlikely to alter the course of a multi-sided war which has killed at least half a million people in the past seven years.
That in turn raises the question of where Western countries go from here, after a volley of strikes denounced by Damascus and Moscow as at once both reckless and pointless.
By morning, the Western countries said their bombing was over for now. Syria released video of the wreckage of a bombed-out research lab, but also of President Bashar al-Assad arriving at work as usual, with the caption "morning of resilience".
There were no immediate reports of casualties, with Damascus allies saying the buildings hit had been evacuated in advance.
British Prime Minister Theresa May described the strike as "limited and targeted". She said she had authorised British action after intelligence indicated Assad's government was to blame for gassing the Damascus suburb of Douma a week ago.
In a speech she gave a vivid description of the victims of the chemical strike that killed scores, huddling in basements as gas rained down. She said Russia had thwarted diplomatic efforts to halt Assad's use of poison gas, leaving no option but force.
French President Emmanuel Macron said the strikes had been limited so far to Syria's chemical weapons facilities. Paris released a dossier which it said showed Damascus was to blame for the poison gas attack on Douma, the last town holding out in a rebel-held swathe of territory near Damascus which government forces have recaptured in this year's biggest offensive.
Washington described its targets as a centre near Damascus for the research, development, production and testing of chemical and biological weapons, a chemical weapons storage site near the city of Homs and another site near Homs that stored chemical weapons equipment and housed a command post.
US Defence Secretary Jim Mattis called the strikes a "one time shot", although Trump raised the prospect of further strikes if Assad's government again used chemical weapons.
Assad's government and allies responded outwardly with fury to Saturday's attack, but also made clear that they considered it a one-off, unlikely to harm Assad in any meaningful way.
Russia, whose relations with the West have deteriorated to levels of Cold War-era hostility, has denied that last week's chemical weapons attack took place and even accused Britain of staging it to whip up anti-Russian hysteria.
President Vladimir Putin called for a meeting of the UN Security Council to discuss what Moscow decried as an unjustified attack on a sovereign state. Syrian state media called the attack a "flagrant violation of international law." An official in Iran's Revolutionary Guards said it would cause consequences against US interests.
Arab states, generally hostile to Assad and Iran, backed the Western action, including both Saudi Arabi and its rival Qatar.