US officials said Russian forces were informed ahead of the attack on the Shayrat airfield near the city of Homs
The US has attacked a Syrian airbase with around 60 Tomahawk missiles in response to the deadly chemical weapons attack in Idlib Province.
Officials have said the missiles were fired from two warships in the Mediterranean Sea.
The attack targeted the Syrian government-controlled Shayrat airfield near the city of Homs - believed by security officials to have been the base for Tuesday’s chemical attack - which killed at least 80 people.
Tonight I ordered a targeted military strike...... pic.twitter.com/3nUzrdiGzX— President Trump (@POTUS) April 7, 2017
The missiles struck their targets, which also included Syrian aircraft and fuel stations, at 4.40am local time on Friday.
US officials said Russian forces were informed ahead of the attack - which did not target sections of the base where they were believed to be present.
Russia has called an emergency meeting of the UN Security Council later today.
US President Donald Trump has called on world leaders to help end what he described as the “slaughter and bloodshed” in Syria.
In an address to the nation, US President Donald Trump said he had ordered a "targeted military strike on an airfield in Syria from where the chemical attack was launched."
He described the strike on Syria as being in the "vital national security interests of the US to prevent and deter the spread and use of chemical weapons."
"Years of previous attempts at changing Assad's behaviour have all failed - and failed very dramatically,” he said.
"As a result the refugee crisis continues to deepen and the region continues to destabilise, threatening the US and its allies."
The intervention raises the risk of confrontation with Russia and Iran, Assad's two main military allies.
Russia has backed the regime since September 2015, also using its veto power in the UN Security Council on several occasions to prevent sanctions against Damascus.
The Kremlin has condemned the strike - with a spokesman for Russian President Vladimir Putin, calling it "an act of aggression against a sovereign nation."
Syrian state TV described the US strike on Friday morning as "American aggression" - with a Syrian military source quoted as saying the strike had "led to losses."
Four soldiers are believed to have been killed by the strike.
The governor of Homs province, Talal Barazi, said the US strikes had served the goals of "armed terrorist groups" and Islamic State, adding that the Syrian leadership and policy "will not change."
He said he believed the "human casualties are not big but there is material damage."
Mr Trump had earlier described Syria's chemical attack in the town of Khan Sheikhoun, Idlib, as "one of the truly egregious crimes" that "shouldn't have happened and it shouldn't be allowed to happen."
The Syrian government has denied being behind that attack and the Russian government had warned against apportioning blame until an investigation had been carried out.
US Secretary of State Rex Tillerson said that the US strikes were "proportionate" and showed that President Trump was willing to act when other countries "cross the line."
He also blamed Russia for failing to uphold a 2013 agreement to secure Syria's chemical weapons, saying Moscow had been either "complicit or incompetent."
President Trump's predecessor Barack Obama had threatened to attack Assad's forces for previous chemical weapons attacks, but never went ahead.
Sky News US Correspondent Cordelia Lynch said: "This is months after Donald Trump said he wouldn't intervene in Middle Eastern wars - he didn't want to get involved in the affairs of other nations.
"It is very unclear at this stage what the potential consequences will be."
Additional reporting from IRN ...