The British Prime Minister's defended sending British warplanes to bomb chemical weapons targets in Syria at the weekend.
Addressing MPs, Theresa May also said Russia's veto on a UN resolution for an independent investigation left no other option.
Opposition parties argue that Parliament should have been consulted first.
Meanwhile, EU foreign ministers have said they understood the need for military action - as they called for renewed efforts for a political solution to the crisis.
The UK leader said Britain along with France and America wanted to stop the further use of chemical weapons.