The French President Emmanuel Macron said the strikes had been limited to Syria's chemical weapons facilities despite reports from pro-Assad commanders of attacks on other targets in the country.
The attack came hours after US President Donald Trump confirmed he'd organised a strike on Damascus.
But she also drew a link with the nerve agent attack on Russian former spy Sergei Skripal and his daughter Yulia in Salisbury.
Peter Felstead, editor of Jane's Defence Weekly military magazine, said the strikes were specifically about chemical weapons use and were not about "wider geopolitical goals".
"There is no proof that the Assad regime is responsible for the chemical attack on civilians", Batten said, referring to the Syrian government headed by Syrian President Bashar al-Assad.
"Assad's recent attack - and today's response - are the direct result of Russia's failure to keep that promise", Trump said.
"This collective action sends a clear message that the global community will not stand by and tolerate the use of chemical weapons", she said.
In attacks alongside U.S. and French allies on Saturday, four British Tornado jets fired Storm Shadow missiles at a Syrian military base suspected of holding chemical weapons ingredients. Trump said strikes on Syria are under way. But she declined to give any signal about the future of Assad.
Military bases near the capital Damascus and the city of Homs were targeted, after an alleged chemical attack on the Syrian town of Douma.
"This is the first time as Prime Minister that I have had to take the decision to commit our armed forces in combat - and it is not a decision I have taken lightly", she said. Moscow has denied any involvement.
In Douma last Saturday, a chemical weapons attack killed up to 75 people, including young children, in circumstances of pure horror.
"The objective of our actions tonight is to establish a strong deterrent against the production, spread and use of chemical weapons", Trump said.
British lawmakers voted down taking military action against Damascus in 2013, in what was widely viewed as an assertion of parliamentary sovereignty on the use of force.
Meanwhile, Britain's main opposition Labour leader Jeremy Corbyn described the USA -led military strikes on Syria jointly staged by three leading Western countries as a "legally questionable action", saying that the British government should "not taking instructions from Washington".
"Corbyn will rail against military action, claiming it could widen the conflict, but if he won't sanction military action against a regime that is using chemical weapons on its own people, when would he ever sanction it?" he told AFP.
"We can not allow the use of chemical weapons to become normalised - either within Syria, on the streets of the United Kingdom or elsewhere", May told reporters in Downing Street.
"Bombs won't save lives or bring about peace", Jeremy Corbyn, leader of the main opposition Labour Party, said in a statement.
"Britain should be playing a leadership role to bring about a ceasefire in the conflict, not taking instructions from Washington and putting British military personnel in harm's way", he said.
British Prime Minister Theresa May described the strike as "limited and targeted".