Explosions lit up the skies over Damascus, the Syrian capital, as Trump spoke from the White House.
Syrian state media said air defenses were activated to block the the attack and published images of smoke clouds hanging over the capital. Defense Secretary Jim Mattis said there were no reports of USA losses in what he described as a heavy but carefully limited assault.
"The evil and the despicable attack left mothers and fathers, infants and children thrashing in pain and gasping for air".
Mixed reactions came from the Middle Eastern countries following an overnight attack on the Assad regime by the U.S., British and French forces.
Mattis, however, said the assault was a "one-time shot", so long as Assad does not repeat his use of chemical weapons.
"A short time ago, I ordered the United States Armed Forces to launch precision strikes on targets associated with the chemical weapons capabilities of Syrian dictator Bashar al-Assad".
The danger is how limited the message is if the operation focuses exclusively on the West's abhorrence for Syria's use of chemical warfare, said John Schanzer, a Middle East and counterterrorism expert who worked as an analyst for the USA department of the treasury.
Syria's air defence system, which mostly consists of systems made in the Soviet Union, has intercepted 71 of the missiles fired on Saturday by the US, British and French forces, he added.
Evidence that the nerve agent sarin also was used is inconclusive, he said.
General Joseph Dunford, chairman of the US Joint Chiefs of Staff, said the allied strikes destroyed three main chemical weapons facilities. The second target was a chemical weapons storage facility west of Homs. "We weren't trying to kill a lot of people", he said. It fulfilled Trump's vow that chemical weapons are a "red line" that he, unlike his predecessor Barack Obama, would not allow Assad to cross.
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. "But our efforts have been repeatedly thwarted" by Syria and Russian Federation, she said.
China said it was "opposed to the use of force" and called for a political solution and a a "return to the framework of worldwide law".
Lebanon has felt the spillover from the Syrian civil war. "It is not about regime change".
Smart missiles should aim terrorists, - Russian Federation reacts to Trump's claim
He wrote Wednesday: 'Our relationship with Russian Federation is worse now than it has ever been, and that includes the Cold War. Here's who Russian Federation has blamed this week for the alleged chemical attack that killed dozens, including many children.
"This is going to set the Syrian chemical weapons program back for years", McKenzie said.
The strikes targeted three areas of Syria: a scientific research center near Damascus, a chemical weapons storage facility west of Homs and a storage facility and command post near Homs.
The strikes were a marked escalation compared with a United States strike following a chemical attack a year ago, when only cruise missiles were used against a single airfield.
Mattis estimated the latest air campaign was about twice the size of the 2017 strike.
"We would have preferred an alternative path, but in this case there was none, " May told reporters in London Saturday morning.
It added that Russian Federation has "undeniably" provided active military support for Damascus and "provided constant political cover to the Syrian regime over the employment of chemical weapons".
"Russia must decide if it will continue down this dark path or if it will join with civilised nations as a force for stability and peace".
"Hopefully, someday we'll get along with Russian Federation and maybe even Iran".
Trump said he had ordered U.S. forces to launch precision strikes "on targets associated with the chemical weapons capabilities of Syrian dictator Bashar al-Assad".
He criticized Washington and its allies for launching the strike without waiting for inspectors from the worldwide chemical-weapons watchdog group to visit the area. He criticized the US and its allies for launching the strike without waiting for global inspectors to visit the area.
China, the fifth permanent member, said through its foreign ministry that it opposed the use of force, urged negotiation and called for a "comprehensive, impartial and objective" investigation into the allegation that chemical weapons were used.
In a statement, it said: "Russia severely condemns the attack on Syria where Russian military are helping the lawful government in the fight with terrorism". "Here we are celebrating to show that you are bankrupt", said a jubilant woman interviewed on state television. "And great warriors they are". Second, it's possible Assad's allies - mainly Russian Federation and Iran - may retaliate against the approximately 2,000 U.S. troops in Syria.
Arkedis said Trump boxed himself in with his impulsive tweeting, in which he signalled a desire to withdraw USA troops from Syria.