US President Donald Trump has hailed an overnight military strike on Syria as "perfectly executed", adding: "Mission Accomplished".
The US, UK and France attacked three government sites, targeting what they said were chemical weapons facilities.
More than 100 missiles struck in response to a suspected deadly chemical attack on the town of Douma last week.
Russian President Vladimir Putin said he condemned the Western strikes "in the most serious way".
Russia, Syria's main ally, had threatened military retaliation if any Russian forces had been hit.
In early morning tweets from Washington, President Trump thanked France and the UK for "their wisdom and the power of their fine military".
A Pentagon briefing on Saturday said the strikes had "set the Syrian chemical weapons programme back for years".
The wave of strikes is the most significant attack against President Bashar al-Assad's government by Western powers in seven years of Syria's civil war.
Responding to the strikes, Mr Assad said in comments published by his office: "This aggression will only make Syria and its people more determined to keep fighting and crushing terrorism in every inch of the country."