She declined to say whether Bashar al-Assad should stay in power and said talks with allies would continue on finding a political solution to the civil war.
"I believe that the action taken will have significantly degraded the Syrian regime's ability to use chemical weapons", she said.
"This action risks not just further escalating the civil war in Syria but also a unsafe escalation of worldwide tensions", said the leader of the left-wing Scottish National Party, the third-biggest force in the British parliament.
The strikes were conducted with the United States and France.
Despite her careful language, there was immediate criticism from opposition lawmakers who said May should have consulted parliament before joining US-led action in Syria.
"There is a wider question on the future political solution for Syria and that is a matter that we will continue to pursue in diplomatic and political channels with our global partners and allies", May said.
"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".
"Last Saturday the Assad regime again deployed chemical weapons to slaughter innocent civilians, this time in the town of Douma near the Syrian capital of Damascus".Читайте также: WhatsApp now allows you to re-download deleted photos and videos
"This legally questionable action risks escalating further.an already devastating conflict", he said, adding that May should have sought parliamentary approval.
The UK has begun air strikes against Syrian chemical weapons sites.
He also did not rule out future military action.
Vince Cable, leader of the Liberal Democrats, said: "Riding the coattails of an erratic USA president is no substitute for a mandate from the House of Commons".
The centre-right Conservatives rely on the support of the Democratic Unionist Party, Northern Ireland's biggest party, for a majority in parliament.
Tom Tugendhat, the Conservative chairman of parliament's foreign affairs scrutiny committee and a former army officer, said May had "taken the correct decision".
"One year ago, Assad launched a savage chemical weapons attack against his own innocent people".
He reiterated that Canada condemns the use of chemical weapons in Ghouta.При любом использовании материалов сайта и дочерних проектов, гиперссылка на обязательна.
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