The British Prime Minister detailed "limited and targeted strikes" on chemical weapons facilities in Syria.
President Donald Trump said the air strikes were in response to the "evil and despicable" chemical attack on April 7 which left "mothers and fathers, infants and children, thrashing in pain and gasping for air".
"There is no practicable alternative to the use of force to degrade and deter the use of chemical weapons by the Syrian regime", she said.
Konashenkov said that Russian Federation knew "for sure" that between April 3-6, the White Helmets - a group which helps civilians in opposition-held territory in Syria - were "under severe pressure specifically from London to produce as quickly as possible this pre-planned provocation".
President Vladimir Putin has said Russian Federation will call an emergency session of the UN Security Council over air strikes on Syria.
"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".
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Vassily Nebenzia, Moscow's UN ambassador, said he "cannot exclude" war between the United States and Russian Federation . Trump said he was prepared to sustain the response until Assad's government stopped its use of chemical weapons .
"Let these united actions send a clear message to the regime - the use of chemical weapons is categorically unacceptable and you will be held to account".
"I think it is right that the global community has come together and said we will not accept this", she added.
Four Royal Air Force Tornado jets using Storm Shadow missiles had taken part in the attack on a military facility near Homs where it was assessed Syria had stockpiled chemicals, Britain's Ministry of Defence (MoD) said.
The air strikes were in retaliation for an alleged chemical attack in Douma earlier this week, which saw horrific images of its aftermath broadcast worldwide.
"While the full assessment of the strike is ongoing, we are confident of its success", she added.
Russia, which intervened in the war in 2015 to back Assad, has denied there was a chemical attack and has accused Britain of helping to stage the Douma incident to stoke anti-Russian hysteria.
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Former PM David Cameron, who lost a vote in 2013 on taking action in Syria, said Mrs May was right to take action.
"We have. evidence that proves Britain was directly involved in organising this provocation", defence ministry spokesman Igor Konashenkov said.
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.
Prime Minister Justin Trudeau said in a statement that Canada stands with its allies and that it supports the decision " to take action to degrade the Assad regime's ability to launch chemical weapons attacks against its own people".
"It was both right and legal to take military action together with our closest allies to alleviate further humanitarian suffering by degrading the Syrian regime's chemical weapons capability", May said.
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