US President Donald Trump has confirmed he ordered a surprise airstrike of cruise missiles on a Syrian airfield in retaliation for Tuesday's alleged chemical weapons attack.
Mr Trump said there was "no dispute" that the Assad regime had used a deadly nerve agent as he called on "all civilised nations in seeking to end the slaughter and bloodshed in Syria".
In a televised statement, he said the deadly strike near Homs - the first direct American attack on the Syrian government of his presidency - was in the "vital national security interest".
He added that the US must "prevent and deter the spread and use of deadly chemical weapons" as the Pentagon released footage of the launch of the missiles from the Mediterranean Sea.
The Pentagon confirmed 59 tomahawk missiles were fired from US Navy destroyers, targeting the air base in Sharyat from where the US says the Syrian forces' planes took off in Tuesday's attack.
At least five people were killed and seven wounded in the airstrike, the governor of Homs province reportedly said.
Talal Barazi, who was quoted by Lebanese TV channel al-Mayadeen, said the attack had caused civilian casualties in a nearby village.
Mr Barazi earlier told the Associated Press the strike had left the air base ablaze as rescue teams sought to reach and evacuate casualties.
Syrian state TV said the airstrikes - which it reported as US "aggression" - had led to "losses" while Syrian rebels welcomed the missile assault.
The military action comes a day after the US president condemned the suspected chemical deaths in Syria as a "disgrace to humanity" that crossed "a lot of lines".
US Secretary of State Rex Tillerson confirmed the US made no contact to Syria's ally Russia ahead of the strikes.
"We sought no approval from Moscow," he said, adding that Russia had "failed to deliver" on preventing chemical weapons being used in the Syria conflict following previous alleged attacks by the Assad regime.
Responding to news of the strikes, ITV News Washington Correspondent Robert Moore tweeted:
Mr Tillerson said the strikes showed the president was prepared to take decisive action in response to heinous acts.
Tuesday's alleged gas attack is believed to have killed at least 72 people, including 20 children.
Speaking from Florida on Thursday night, where Mr Trump is hosting Chinese President Xi Jinping, the president evoked the images of children dying in a calm but emotional address to the nation.
"Assad choked out the lives of helpless men, women and children. It was a slow and brutal death for so many. Even beautiful babies were cruelly murdered in this very barbaric attack," he said.
"Tonight I ordered a targeted military strike on the airfield in Syria from where the chemical attack was launched.
"It is in this vital national security interest of the United States to prevent and deter the spread and use of deadly chemical weapons."
The airfield strikes targeted an airstrip, an aircraft and fuel stations after being fired from Navy destroyers in the eastern Mediterranean.
Syrian state TV labelled the attacks as an "aggression" as it reported strikes on a number of military targets.
The surprise strikes at around 8.45pm Washington time came a day after Downing Street had played down the prospect of military action.
Number 10 had insisted "nobody is talking" about an armed response to the atrocity as the UK issued a call for diplomatic action in response to the attack.