The missile strike against a Syrian airbase marks the first time the United States has directly attacked the regime of President Bashar al-Assad.
Here is what we know so far about the target and the outcome of the strike.
- The target -
At around 3:40 am Syria time on Friday (0040 GMT) the US military fired 59 Tomahawk missiles at the Shayrat airfield near Homs in central Syria.
According to the Pentagon, as well as hosting Syrian aircraft the facility was used to store chemical weapons.
The Tomahawks targeted aircraft, hardened aircraft shelters, petroleum and logistical storage, ammunition supply bunkers, air defence systems and radars, the Pentagon said.
Pentagon spokesman Navy Captain Jeff Davis said the strike lasted "a couple of minutes."
US intelligence agents believe aircraft from Shayrat conducted a suspected chemical weapons attack on April 4.
National Security Advisor H.R. McMaster said measures had been put in place to avoid hitting sarin gas stored at the airfield.
"So that would not be ignited and cause a hazard to civilians or anyone else," McMaster said.
- How it was launched -
The strike was launched from the destroyers USS Porter and USS Ross in the eastern Mediterranean.
Russian forces were warned ahead of the strike using a special military-to-military hotline.
Davis said the strike was designed to avoid casualties.
"Every precaution was taken to execute this strike with minimal risk to personnel at the airfield," he said.
- The result -
According to the Pentagon, initial indications showed the strike had severely damaged or destroyed Syrian aircraft, infrastructure and equipment at Shayrat.
The Syrian army in a statement said six people were killed at the base and that the attack caused "significant damage".
The SANA state news agency said four children were among nine civilians killed in surrounding villages.
US officials stressed the strike was a direct reaction to the chemical attack, and not the beginning of a broader military campaign against Assad.
"The strike was a proportional response to Assad's heinous act," Davis said.
Russian state television said that nine planes have been destroyed at the base, but that the runway was intact.
Davis said the runways themselves were not targeted.
- Legal concerns -
The strike was launched at the order of President Donald Trump and was a "proportional response," Davis said.
But critics questioned whether the action amounted to a declaration of war and said Trump should have gone to Congress first.
America is currently hitting the Islamic State group in Syria under a 2001 Authorization for the Use of Military Force.
But Damascus government ally Russia said the strike constituted an "aggression against a sovereign state" and suspended a bilateral agreement to help avoid clashes in the skies over Syria.