Here is the full text of her statement:
"This evening I have authorised British armed forces to conduct co-ordinated and targeted strikes to degrade the Syrian regime's chemical weapons capability and deter their use.
"We are acting together with our American and French allies. In Douma, last Saturday, a chemical weapons attack killed up to 75 people, including young children, in circumstances of pure horror.
"The fact of this attack should surprise no-one. The Syrian regime has a history of using chemical weapons against its own people in the most cruel and abhorrent way.
"And a significant body of information including intelligence indicates the Syrian regime is responsible for this latest attack.
"This persistent pattern of behaviour must be stopped - not just to protect innocent people in Syria from the horrific deaths and casualties caused by chemical weapons but also because we cannot allow the erosion of the international norm that prevents the use of these weapons.
"We have sought to use every possible diplomatic channel to achieve this.
"So there is no practicable alternative to the use of force to degrade and deter the use of chemical weapons by the Syrian Regime. This is not about intervening in a civil war. It is not about regime change.
"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.
"At this time, my thoughts are with our brave British servicemen and women - and our French and American partners - who are carrying out their duty with the greatest professionalism.
"The speed with which we are acting is essential in co-operating with our partners to alleviate further humanitarian suffering and to maintain the vital security of our operations.
"This is the first time as Prime Minister that I have had to take the decision to commit our armed forces in combat - and it is not a decision I have taken lightly.
"I have done so because I judge this action to be in Britain's national interest.
"We cannot allow the use of chemical weapons to become normalised - within Syria, on the streets of the UK, or anywhere else in our world. We would have preferred an alternative path. But on this occasion there is none.
"History teaches us that the international community must defend the global rules and standards that keep us all safe. That is what our country has always done. And what we will continue to do."
(Except for the headline, this story has not been edited by NDTV staff and is published from a syndicated feed.)
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