Loud explosions rocked Syria's capital and filled the sky with heavy smoke early Saturday after US president Donald Trump announced airstrikes in retaliation for the country's alleged use of chemical weapons.
Syrian air defences responded to the joint strikes by the United States, France and Britain.
Smoke was seen rising from east Damascus and the lit-up sky turning orange for the blasts while a huge fire could be seen from a distance to the east.
Syrian television said the attacks targeted a scientific research centre in Barzeh, near Damascus, and an army depot near Homs while it was reported air defences had hit 13 incoming rockets south of Damascus.
After the attack ceased and the early morning skies went dark once more, vehicles with loudspeakers roamed the streets of Damascus blaring nationalist songs.
"Good souls will not be humiliated," Syria's presidency tweeted after airstrikes began.
Syrian state TV called the attacks a "blatant violation of international law and shows contempt for international legitimacy".
The US president said Washington is prepared to "sustain" pressure on Mr Assad until he ends what the president called a criminal pattern of killing his own people with internationally banned chemical weapons.
The decision to strike, after days of deliberations, marked Mr Trump's second order to attack Syria.
He had previously 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.
Mr Trump chastised Syria's two main allies, Russia and Iran, for their roles in supporting "murderous dictators," and noted that Russian president Vladimir Putin had guaranteed a 2013 international agreement for Mr Assad to get rid of all of his chemical weapons.
He called on Moscow to change course and join the West in seeking a more responsible regime in Damascus.
Russia's US embassy released a statement warning that the airstrikes will "not be left without consequences", adding that "all responsibility" rests with Washington, London and Paris.
In his nationwide address, Mr Trump stressed that he has no interest in a longtime 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."
The US has about 2,000 troops on the ground in Syria as advisers to a makeshift group of anti-Islamic State fighters known as the Syrian Democratic Forces.
They are in eastern Syria, far from Damascus. A US-led coalition has been conducting airstrikes in Syria since September 2014 as part of a largely successful effort to break the IS grip on both Syria and Iraq.