It is the first US intervention in Syria's six-year war - missile strikes on an airbase in response to the chemical weapons attack on civilians.
The gas attack has been blamed on the regime of Bashar al Assad, although the Syrian government has denied using chemical agents.
Here, we take a look at the key players in the Syrian president's inner circle.
President Bashar al Assad
The 51-year-old initially, trained as a doctor, and as a postgraduate spent time in London specialising in eye problems.
His elder brother Bassel, the heir apparent to their father Hafez al Assad, was killed in a car crash in 1994.
Bashar succeeded his father as president in July 2000.
Originally touted as a potential reformer, his part in the crackdowns on Arab Spring protesters, which led to the Syrian Civil War, led to calls from the EU and US for him to stand down.
In 2013, the UN directly implicated Mr Assad in war crimes for his role in the Syrian conflict.
In 2017, he was named on a list produced by the International Criminal Court (ICC) as one of the 15 people "to be scrutinised in relation to use of CW (chemical weapons) by Syrian Arab Republic Armed Forces in 2014 and 2015".
His wife, Syria's first lady Asma al Assad , who was born in Acton and educated at King's College London, said during an interview last year that she has been offered "financial security" outside of Syria, but refused to leave as she did not want to "shatter people's confidence in their president".
Maher al Assad, military commander
Mr Assad's younger brother and right-hand man commands the army's elite fourth armoured division.
The 49-year-old appeared to have been demoted to 'Brigadier General' in 2016, but in January 2017 he was promoted to the rank of Major General.
He reportedly lost a leg during an attack on Syria's security cabinet in Damascus in 2012.
He is also named on the ICC chemical weapons list.
Walid al Mouallem, foreign minister
Mr Mouallem became foreign minister in 2006.
He led the Syrian official government delegation to peace negotiations in Geneva with representatives of the opposition, but two rounds of peace talks mediated by the UN failed to bring the sides closer.
Mr Moualem has denied government involvement in the chemical assault on Khan Sheikhoun.
He echoed the Russian government's claim that the army bombed an arms depot belonging to al Qaeda affiliate, the al Nusra Front, now known as the Fateh al Sham Front.
General Issam Hallaq, Syrian Air Force chief
Mr Hallaq took the role of air force chief of staff in 2010. The EU imposed sanctions on Mr Hallaq in 2012 and he's also named on the ICC chemical weapons list.
Dr Najah al Attar, vice president of Syria
Born in 1933, Ms Attar is from a Sunni family, and the first woman to hold such a high position in Syria.
She gained a diploma in Islamic studies from the University of Damascus before obtaining a PhD in Arabic literature from the University of Edinburgh in 1958.
After returning from the UK, she taught at schools in Damascus before being appointed the minister of culture from 1976 to 2000.
She became joint Vice-President in 2006 but some reports suggest she is out of favour for advocating a negotiated solution to the conflict.
Faruq al Sharaa, vice president (joint role held with Ms Attar)
Mr Sharaa served as Foreign Minister for 22 years before becoming Vice- President.
His preference for a negotiated solution to the Syrian conflict, rather than the president's strategy of crushing the revolt militarily, has also led to reports he is no longer on good terms with Mr Assad.
General Muhammad al Mahalla, head of military intelligence
Mr Mahalla has been head of the internal affairs branch of Syria's Military Intelligence since April 2016.
The EU has accused him of being "responsible for repression and violence against the civilian population in Damascus".
The EU added his name to its sanctions list in 2015 and he is also named on the ICC chemical weapons list.
Rami Makhlouf, businessman
The maternal cousin of Assad, Mr Makhlouf is widely considered to be one of the most influential men in Syria.
The Syrian billionaire was granted citizenship of Cyprus in 2011, which was later extended to his wife and three sons.
However, this was withdrawn from the whole family in 2012.
He has been under US sanctions since 2008 for "public corruption" and under EU sanctions since May 2011 under accusations of bankrolling Mr Assad.
With previous business interests in banking, mobile phones and real estate, in June 2011 he announced he was quitting the Syrian business scene and becoming a philanthropist.
Fahd Jassem al Freij, defence minister and deputy prime minister
Taking office in July 2012, the former chief of staff replaced Dawoud Rajiha after he was assassinated in 2012 in the Damascus bombing.
Mr Freij has a military background and joined the Syrian Arab Army in 1968.
A report released by Amnesty International on 7 February 2017 alleged Mr Freij was complicit in the killings of up to 13,000 individuals tried and convicted in secret military courts.
The report says Mr Freij's signature, or that of the Syrian Chief of the General Staff, was one of two needed for a death warrant issued by the secret courts to be implemented, and also that he witnessed the executions of those condemned by the military courts on several occasions.
He is also named on the ICC chemical weapons list.