- Video report by ITV News Political Correspondent Carl Dinnen
Theresa May is to face questions from MPs in an an emergency debate in the House of Commons over her decision to launch joint US-UK-French military action in Syria.
The Prime Minister will reiterate her belief that the overnight strikes on chemical weapons plants was in Britain's "national interest".
Downing Street has already published a document outlining why it believes the military intervention was legal however the PM is expected to face anger in the commons.
Opposition figures, including Jeremy Corbyn, have questioned why Mrs May gave the go ahead to the strikes without Parliamentary approval.
Foreign Secretary Boris Johnson insisted the strikes were "right for the UK and right for the world".
The Russian president Vladimir Putin made clear his opinion that further airstrikes against Syria would "inevitably" set international relations on a collision course.
In a conversation with Iran's president Hassan Rouhani, President Putin reiterated Moscow's belief that the overnight strikes against Syria were "illegitimate" - adding that the prospects for a political settlement to the civil war had been seriously damaged.
The Kremlin's comments came after the US indicated that it would be willing to launch fresh strikes should the Assad regime carry out further chemical weapons attacks.
Mr Johnson, speaking at a summit of European Union foreign ministers, stressed the strikes were "not an attempt to change the tide of the war in Syria or to have regime change" and "the Syrian war in many ways will go on in its horrible, miserable way".
"But it was the world saying that we have had enough of the use of chemical weapons, the erosion of that taboo that has been in place for 100 years has gone too far under Bashar Assad," he said.
In a statement on the Putin-Rouhani conversation, Moscow said: "The two leaders exchanged opinions on the situation following missile strikes carried out by the United States and their allies on Syrian territory.
"The presidents stated that this illegitimate action has seriously damaged the prospects for a political settlement in Syria.
"Vladimir Putin, in particular, emphasised that if such actions continue in violation of the UN Charter, this will inevitably lead to chaos in international relations."
Relations between Russia and the West have particularly soured over the past weeks in the wake of Salisbury spy attack and alleged chemical attack in Douma.
On Friday night the US, Britain and France launched airstrikes against Syrian chemical sites after obtaining "proof" that poisonous gas was used last weekend in Douma, killing 41 civilians.
Russia and Syria claim the attack was fabricated.
Mr Johnson said action had to be taken against Syria for the Douma attack.
"The overwhelming why this was the right thing to do, and that is to deter the use of chemical weapons - not just by the Assad regime - but around the world," Mr Johnson said, speaking on The Andrew Marr Show on Sunday.
He added: "You can imagine that people around the world are looking now and saying 'finally, someone stood up against that.
"And the world said 'enough' to the use of such weapons."
Yesterday Mrs May insisted the military action was "legal" and defended the decision to go ahead without securing the backing of Parliament.
Addressing the commons today, she will say: "We are confident in our own assessment that the Syrian regime was highly likely responsible for this attack and that its persistent pattern of behaviour meant that it was highly likely to continue using chemical weapons."
The airstrikes, carried out by the US, UK and French military, targeted three separate targets in Syria linked to the Assad regime's chemical weapons program.
Last night the UN Security Council rejected a resolution tabled by Russia calling for condemnation of the "aggression" by the United States and its allies against Syria.
Theresa May will tell the commons that Germany, Italy, Canada, Australia and European Council president Donald Tusk have "all expressed their support for the actions that Britain, France and America have taken".
Meanwhile Labour leader Jeremy Corbyn has said Parliament should have been given a vote ahead of the strikes.
"I think what we need in this country is something more robust like a War Powers Act so that governments do get held to account by Parliament for what they do in our name," he told The Andrew Marr show.
However International Development Secretary Penny Mordaunt opposed calls from Mr Corbyn to give Parliament greater powers over military interventions.
Ms Mordaunt told BBC Radio 4's Today: "To take a decision on whether something is legally justified, and whether what we are actually intending on doing in terms of targets is appropriate, you would need to know information that could not be shared with every MP."
She added that it would be a "crazy thing to do" to share information on targets with MPs.