But she avoided answering questions on her future strategy for Syria, on whether parliament would be consulted on any further strikes and ignored demands by Corbyn for a War Powers Act to limit the government's power to launch military action.
But her move to add British Tornado jets to US and French forces that launched around 105 missiles in the early hours of Saturday might be met with retaliatory measures by Syrian ally Russian Federation and breaks with a convention to obtain parliamentary approval for military action dating back to the 2003 Iraq war.
She went on to list the evidence that Syrian regime had to be behind the attack, including witness and NGO reports, as well as the fact that the military hardware required for such an attack could not have come from "Islamic State" terrorists or other Syrian rebels.
The UK leader has addressed MPs in the House of Commons over her decision to launch airstrikes in Syria without parliamentary approval.
The leaders of the opposition Scottish National Party and Liberal Democrats have also criticised May and there is the possibility of a vote in parliament later Monday that could embarrass the prime minister if she loses.
"But it is my responsibility as prime minister to make these decisions and I will make them".More news: Starbucks Issues Apology Over Philadelphia Store Arrests
Speaking to the BBC, Johnson said what he described as the successful strikes on three sites in Syria were a message from the world that enough was enough, but acknowledged he could not say whether Assad still had chemical weapons.
"We have done this because we believe it is the right thing to do, and we are not alone".
May will make a statement on the action to the House of Commons on Monday, but opposition lawmakers have lined up to call for a more meaningful debate and a possible retrospective vote on the action, which would severely test her position.
Ahead of May's speech in parliament, Foreign Secretary Boris Johnson on Monday said the strikes were "right for the United Kingdom and right for the world" ahead of talks with European Union foreign ministers.
A third event called Don't Bomb Syria starts at 5.30pm in Bedford Square Exeter.
Britain has said there are no plans for future strikes against Syria. This was a limited, targeted strike on a legal basis that has been used before.More news: Pence abruptly leaves summit, Trump to speak
But she will be mindful of how military action can backfire.
"There's no more serious issue than the life-and-death matter of military action, and Parliament has the right to support or stop the government taking military action".
Former Prime Minister Tony Blair's legacy was tainted by his decision to join the war against Iraq, especially after an inquiry concluded that the decision was based on flawed intelligence, while her predecessor, David Cameron, was damaged after losing a vote for strikes against Syria in 2013.
The poll by Survation for the Mail on Sunday showed 36 percent in favour of Britain's participation in the air strikes, 40 percent against and the remainder undecided.
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