Cruise missile strikes against the Syrian regime should act as a warning to Russia over its use of chemical weapons, Theresa May has said.

The Prime Minister insisted that joining the bombing campaign with the United States and France was the “right thing for us to do” in the wake of the “harrowing” assault on Douma a week ago.

Mrs May said the military action was “legal” and defended the decision to go ahead without securing the backing of Parliament.

But she was accused of “riding the coat-tails of an erratic US president” by the Liberal Democrats, and “taking instructions” from Washington by Labour.

Four Royal Air Force Tornados GR4s joined the co-ordinated missile strikes at 2am, launching Storm Shadow missiles at a base 15 miles west of Homs.

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Prime Minister Theresa May during a press conference in Downing Street on the air strikes against Syria (Simon Dawon/PA)

The Prime Minister said the Cabinet had taken advice from the Attorney General, National Security Adviser and military chiefs when it met on Thursday.

She added: “We agreed that is was both right and legal to take military action together with our closest allies.”

Mrs May said “it was right we acted the way that we did” for operational security reasons to help protect the military.

She insisted the action against Bashar Assad’s regime was a limited and targeted strike to degrade and deter the Syrian government and was not about regime change.

But she also drew a link with the nerve agent attack on Russian former spy Sergei Skripal and his daughter Yulia in Salisbury.

Looking drawn as she spoke to reporters in Downing Street in a hastily arranged press conference, she said: “We cannot allow the use of chemical weapons to become normalised – either within Syria, on the streets of the UK or elsewhere.”

Vladimir Putin has said Russia will call an emergency session of the UN Security Council over the strikes on Syria.

The Russian president said they were an “act of aggression” that would have a “destructive” influence on international relations.

Asked if the strikes had also been a warning to Russia, Mrs May said: “The action that took place last night was an action which was focused on degrading and deterring the operational capability and the willingness of the Syrian regime to continue to use chemical weapons.

“There have been many instances when we have seen them using those chemical weapons.

“But I believe it should also be a message to others that the international community is not going to stand by and allow chemical weapons to be used with impunity.”

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An RAF Tornado taxis into its hangar at RAF Akrotiri in Cyprus after taking part in the strikes (Cpl L Matthews/MoD/PA)

The PM said chemical weapons had “all too often” been used in recent times.

“I think it is right that the international community has come together and said we will not accept this,” she added.

US President Donald Trump announced the “combined operation” on Friday night and Mrs May spoke soon afterwards to explain her decision.

Jeremy Corbyn said the military action against Syria was “legally questionable” and makes real accountability for war crimes less likely.

The Labour leader said he would be pushing for the Government to release the legal advice it received ahead of the strikes.

Number 10 is expected to put out a summary of the advice it received later on Saturday, Downing Street sources said.

He said: “Bombs won’t save lives or bring about peace. This legally questionable action risks escalating further, as US defence secretary James Mattis has admitted, an already devastating conflict and therefore makes real accountability for war crimes and use of chemical weapons less, not more likely.”

Bombs won’t save lives or bring about peace.This legally questionable action risks escalating further, as US defence…

Posted by Jeremy Corbyn on Saturday, April 14, 2018

Mrs May has faced criticism from across the political spectrum for failing to recall Parliament and put the plans to a vote.

The Prime Minister said she will go before the Commons on Monday to answer questions about her decision but insisted there was no “alternative path”.

On Friday, Russian military chiefs claimed they had evidence the UK had directed the attack in Douma using the White Helmets, a group of humanitarian volunteers on the ground.

Mrs May said the accusation was “grotesque and absurd” as she criticised Russia for vetoing at the UN calls for an independent investigation.

The PM did not rule out further action if Syria continues to use chemical weapons.

Mr Trump said the Syrian regime’s use of chemical weapons on Douma was a “significant escalation in a pattern of chemical weapons use by that very terrible regime”.

Following the announcement, the US said strikes had been launched at 9pm EST (2am BST) and had destroyed important infrastructure at three sites connected with the Syrian regime’s chemical weapons programme.

General Joseph Dunford, chairman of the US Joint Chiefs of Staff, said the first was at a scientific research centre in greater Damascus, involved in the development and production of chemical warfare.

Other strikes targeted an army depot near Homs.