In a statement Friday night, U.S. President Donald Trump outlined strikes being carried out against the Syrian regime of Bashar al-Assad after a chemical weapon attack earlier in the week.
She added: "Russia can complain all it wants about fake news but no-one is buying its lies and its cover-ups".
"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".
In an unusual move, the Prime Minister will gather her most senior ministers in Number 10 to update them on the latest developments in the crisis, despite the fact that Parliament is still in recess.
May seemed determined to resist calls for a retrospective vote on her actions, saying only that Parliament "will get an opportunity to question me" after she has made a statement on the attacks on Monday.
Syrian air strikes: Read Donald Trump and Theresa May's statements in full
U.S. President Donald Trump said he was prepared to sustain the response until the government of Assad stopped its use of chemical weapons.
At an emergency meeting of the UN Security Council, US ambassador Nikki Haley warned if there was further use of chemical weapons in Syria, America is "locked and loaded".
May will tell MPs: "Let me be absolutely clear: we have acted because it is in our national interest to do so".
"All the indications are that the Syrian regime was responsible", May said.
US Defence Secretary Jim Mattis, striking a cautious tone after Mr Trump's threat of missile strikes, said on Wednesday the United States was still assessing intelligence about the suspected toxic gas attack.
By launching strikes without prior approval from Parliament, Mrs May dispensed with a non-binding constitutional convention dating back to the 2003 invasion of Iraq.
Britain has accused Russian Federation of being behind last month's nerve agent attack on former spy Sergei Skripal and his daughter in Salisbury, southern England - a charge Moscow has denied.
"We can not allow the use of chemical weapons to become normalized - either within Syria, on the streets of the United Kingdom or elsewhere", May told reporters in Downing Street.
"We will need to take decisions in due course, when we judge it most useful and effective", Mr Macron said.
The UK has begun air strikes against Syrian chemical weapons sites. The United States responded with 58 missile strikes that destroyed 20% of the Syrian airforce.
May has not confirmed whether Britain will participate directly but said "the continued use of chemical weapons can not go unchallenged".
May dismissed as "grotesque and absurd" a claim by Russian Federation, which intervened in the war in 2015 to back Assad, that the Douma attack was staged by Britain.
"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". He said earlier this week that France was ready to attack the "chemical capabilities" of the Assad regime.
Many politicians in Britain, including some in Mrs May's own Conservative Party, had called for Parliament to be recalled from holiday to give authority to any military strike.
Parliament voted down British military action against Assad's government in 2013, in an embarrassment for May's predecessor, David Cameron.
Ministers have said it is "highly likely" Assad's regime was responsible for the attack on Saturday on the rebel-held town of Douma which reportedly left dozens dead and that there was agreement around the Cabinet table that such actions should not go "unchallenged".