Brigg and Goole MP Andrew Percy said the conditions on the ground had changed as Islamic State (Isis) had been all but wiped out in Syria.
He spoke as the Prime Minister gave her strongest backing yet to the assessment that Moscow-backed Syrian president Bashar Assad and his forces were responsible for a suspected chemical weapons attack in the rebel-held town of Douma on Saturday.
In a hardening of her language, Mrs May said “all the indications” are that Assad was responsible for the brutal attack.
The Syrian refugee on a mission to save Britain’s beesIt came after Mr Trump launched an astonishing broadside at Russia, which warned against military action and promised to shoot down rockets fired at Syria.
Responding in a trademark tweet, President Trump said: “Russia vows to shoot down any and all missiles fired at Syria.
“Get ready, Russia, because they will be coming, nice and new and ‘smart’. You shouldn’t be partners with a Gas Killing Animal who kills his people and enjoys it!”
The PM will first have to negotiate calls for a House of Commons vote on any military action led by Labour leader Jeremy Corbyn.
But she received a boost as two Tories who rebelled against David Cameron over military action in 2013, Mr Percy and Totnes MP Sarah Wollaston, backed intervention.
Mr Percy told The Yorkshire Post: “We were moving too quickly and the action would likely have aided the spread of Isis which would have resulted in more deaths. Isis are obviously well in retreat and the facts on the ground are wholly different now. As such, we have a responsibility to work with the US and the French to respond.”
Ms Wollaston tweeted: "I did not support military action in the past but chemical weapons are now being used with impunity, including here in UK. It is time to act to stop the use of these horrific weapons."
Another the-rebel, Cleethorpes MP Martin Vickers, said he would have to look at the evidence before making his decision again but did not regret his 2013 decision.
He told this newspaper: "I’m not wholly persuaded that further action would be effective but I will obviously not make a decision until I’ve heard what the Prime Minister and other ministers have got to say.”
Earlier, Mrs May said on a visit to Birmingham: "We are working with our allies, we have been working to get an understanding of what happened on the ground.
“We are rapidly reaching that understanding.
“All the indications are that the Syrian regime was responsible and we will be working with our closest allies on how we can ensure that those who are responsible are held to account and how we can prevent and deter the humanitarian catastrophe that comes from the use of chemical weapons in the future.
“The continued use of chemical weapons cannot go unchallenged.”