Prime Minister Theresa May said the "limited and targeted strike" was part of joint action with France and the United States in response to Syria's latest alleged chemical weapons atrocity.

"There is no practicable alternative to the use of force to degrade and deter the use of chemical weapons by the Syrian regime," May said in a televised statement.

"This is not about intervening in a civil war. It is not about regime change.

"It is about a limited and targeted strike that does not further escalate tensions in the region and that does everything possible to prevent civilian casualties," she said.

May said "a significant body of information including intelligence" pointed to Syrian government responsibility for a suspected chemical attack in Douma last Saturday.

She said the strikes would "send a clear signal to anyone else who believes they can use chemical weapons with impunity".

"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.

"I have done so because I judge this action to be in Britain's national interest," she added.

In her comments, May also alluded to a nerve agent attack in Britain last month on a former Russian spy and his daughter.

"We cannot allow the use of chemical weapons to become normalised -- within Syria, on the streets of the UK, or anywhere else in our world," she said.

Britain has blamed Russia for the poisoning -- a charge vehemently denied by Moscow which has accused London of failing to come up with evidence for its claims.

- 'Meticulous target planning' -

Britain's defence ministry said in a statement that four British Tornado jets had fired Storm Shadow missiles at the base 15 miles (24 kilometres) west of Homs at 0100 GMT.

The ministry said the facility was "a former missile base... where the regime is assessed to keep chemical weapon precursors".

"Initial indications are that the precision of the Storm Shadow weapons and meticulous target planning have resulted in a successful attack," it said.

"Very careful scientific analysis was applied to determine where best to target the Storm Shadows to maximise the destruction of the stockpiled chemicals and to minimise any risks of contamination to the surrounding area.

"The facility which was struck is located some distance from any known concentrations of civilian habitation, reducing yet further any such risk," it added.

May held an emergency cabinet meeting to discuss possible action on Thursday and there had been calls for the British parliament to be consulted before any air strikes.

Parliament is not due to reconvene until Monday, following its Easter recess.

Polls in recent days have shown public wariness of military intervention in Syria, with Britain still haunted by its participation in the US-led invasion of Iraq.

A YouGov poll in The Times conducted this week found that 43 percent of voters opposed strikes in Syria, with 34 percent unsure and only 22 percent supportive.

- 'Gesture bombing' -

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.

But they backed action in Iraq the following year, and again in Syria in 2015, strictly limiting strikes to targets of the Islamic State group.

Britain continues to support the US-led coalition targeting IS jihadists in Iraq and Syria, and has conducted more than 1,700 strikes.

Jeremy Corbyn, leader of the main opposition Labour Party, had on Friday accused the government of "waiting for instructions" from US President Donald Trump on what to do over Syria.

"Further UK military intervention in Syria's appalling multi-sided war risks escalating an already devastating conflict," he said.

Following the air strikes, there was criticism from some opposition MPs.

Stewart McDonald of the Scottish National Party said: "The PM has engaged UK forces in gesture bombing, with no major international consensus and no long term plan to halt the use of chemical weapons or deliver peace.

"Most worrying, is that she has acted at the behest of presidential tweets and sidelined parliament," he said.

Labour MP Kevin Brennan wrote: "Parliamentary approval should have been sought".