A US official said around 59 precision guided Tomahawk missiles were fired from two warships in the Mediterranean Sea, targeting the Shayrat Airfield in Syria, where Washington believes Tuesday's deadly attack was launched.
"On Tuesday, Syrian dictator Bashar al-Assad launched a horrible chemical weapons attack on innocent civilians. Using a deadly nerve agent, Assad choked out the lives of helpless men, women and children," Trump said in a statement.
"It was a slow and brutal death for so many. Even beautiful babies were cruelly murdered in this very barbaric attack."
Trump said it is in the vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons.
"Years of previous attempts at changing Assad's behaviour have all failed, and failed very dramatically. As a result, the refugee crisis continues to deepen and the region continues to destabilise, threatening the United States and its allies," the American president continued in his statement.
"Tonight, I call on all civilised nations to join us in seeking to end the slaughter and bloodshed in Syria, and also to end terrorism of all kinds and all types."
However, Syrian state TV called the US military strike an act of "aggression," saying the strike caused 'losses' without further elaborating.
"A US act of aggression (was committed) against Syrian military targets, using several missiles," the channel said soon after the US announced the strike.
The United States also said it had warned Russia ahead of the massive military strike.
"Russian forces were notified in advance of the strike using the established deconfliction line," Navy Captain Jeff Davis said, referring to a special military hotline.
"US military planners took precautions to minimise risk to Russian or Syrian personnel located at the airfield."
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Earlier this week, Syrian government aircraft killed dozens of civilians by using chlorine mixed with a nerve agent, possibly sarin.
The bombing represents President Donald Trump's most dramatic military order since taking office. The Obama administration threatened attacking Assad's forces for previous chemical weapons attacks, but never followed through.
Trump did not announce the attacks in advance, though he and other national security officials ratcheted up their warnings to the Syrian government throughout the day on Thursday.
"I think what happened in Syria is one of the truly egregious crimes and shouldn't have happened and it shouldn't be allowed to happen," Trump told reporters travelling on Air Force One to Florida, where he was holding a two-day summit with Chinese President Xi Jinping.
The strike came as Trump was hosting Xi in meetings focused in part on another pressing US security dilemma: North Korea's nuclear programme. Trump's actions in Syria could signal to China that the new president isn't afraid of unilateral military steps. even if key nations like China are standing in the way.