The shadow foreign secretary said she was concerned the move would only “escalate” the war in Syria, after at least 80 people were killed earlier in the week.
She said: “My starting point is – is this going to help with bringing the war to an end? We need to have war bright to an end as soon as possible and that’s really what counts.
“So does this help to bring the war to an end quickly or does it escalate it? And that’s the question really. I’m concerned that it may be escalating it.
Emily Thornberry blasted Donald Trump for acting 'without any evidence'
I don’t think it was right for Donald Trump to decide on his own without consultation with anyone, without any evidence and go ahead and bomb at this stage
“We’ve just heard from the Russian reaction, we’ve just heard haven’t we that the Russians are talking about not cooperating with the Americans in terms of allowing aircraft above ISIS, so there’s going to be problems in terms of fighting ISIS in Syria.”
She said the conflict needed to be settled through “peace talks” and said the UN should have had a faster response to Tuesday’s attack.
Ms Thornberry said: “Look, in the end, the only solution to Syria is for there to be peace talks and a political settlement. So does this attack [the missile strikes] help with that political settlement or does it escalate it?
“What I think we need to be doing is we should have had a fast response from the United Nations looking at and bringing evidence before the Security Council to show, to prove that Assad was responsible for this so that the international community could act together on evidence.
Trump launches military strike against Syria Fri, April 7, 2017
U.S. President Donald Trump launched 59 Tomahawk missiles against Syria in response to its chemical attack on its own civilians
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Trump ordered a massive military strike against a Syria
A US ship conducting a test launch of a tomahawk rocket in 2010
“I think that the best way to proceed is to proceed internationally and to proceed collectively. I don’t think it was right for Donald Trump to decide on his own without consultation with anyone, without any evidence and go ahead and bomb at this stage.”
In a statement, Mr Trump said it was in the “vital national security interests” of the US to “prevent the spread and use of chemical weapons”.
He said: ”There can be no dispute that Syria used banned chemical weapons, violated its obligations under the Chemical Weapons Convention and ignored the urging of the UN Security Council."
The UK has also back the move. A Government spokesman said: "The UK Government fully supports the US action which we believe was an appropriate response to the barbaric chemical weapons attack launched by the Syrian regime and is intended to deter further attacks."
Tensions between America and Syrian ally Russia continue to grow with a spokesman for Vladimir Putin saying the Russian leader regarded the US action as "aggression against a sovereign nation" on a "made-up pretext”.