Defence Secretary Jim Mattis warned such an attack carried the risk of spinning out of control, suggesting caution ahead of a decision on how to respond to an attack against civilians last weekend that US officials are increasingly certain involved the use of banned chemical weapons.
President Trump says he'll make a decision "fairly soon" on whether to launch a missile attack on Syria.
Officials also said that the USA has compiled intelligence from the US and other countries, including images, that indicate the Syrian government was behind the weekend attack.
Britain continues to support the US-led coalition targeting IS jihadists in Iraq and Syria, and has conducted more than 1,700 strikes.
At stake in Syria is the potential for confrontation, if not outright conflict, between the US and Russian Federation, former Cold War foes whose relations have deteriorated in recent years over Moscow's intervention in Ukraine, its interference in the 2016 USA presidential election and, most recently, its support for Syrian President Bashar Assad. In another tweet on Thursday, Trump wrote that an attack on Syria "could be very soon or not so soon at all!"
Citing US estimates that Assad has used chemical weapons "at least 50 times" in the seven-year war, Haley said: "All nations and all people will be harmed if we allow Assad to normalize the use of chemical weapons".
Cabinet ministers have agreed on a "need to take action" against Syria, following a suspected chemical weapon attack that claimed the lives of dozens of people in the Damascus suburb of Douma. Asked if France is planning to participate in retaliatory attacks on Syria, he was noncommittal.
The Syrian government denies responsibility.
It came nearly exactly a year after a chemical attack in the northern Syrian town of Khan Sheikhoun killed dozens of people.
Moisi stressed the "risk of escalation" of the conflict amid increasing concerns about a U.S. -Russia proxy war.
Outlining the reasons why he voted against, he said: "One was because he (Mr Cameron) hadn't provided the evidence and intelligence that we knew who it was, and secondly because there was not a proper plan which was thought through properly". "We need to know where that's going, what the objective of it is before we take that act".
U.S. Defense Secretary James Mattis said Thursday President Donald Trump has yet to decide on whether he will pursue military action in Syria.
Chancellor Angela Merkel said after speaking with Macron on Thursday that Germany won't participate in possible military action in Syria, but supports sending a message that the use of chemical weapons is unacceptable.
The statement made no specific reference to military action.
May is not obliged to win parliament's approval, but a non-binding constitutional convention to do so has been established since a 2003 vote on joining the USA -led invasion of Iraq. This is in contrast to an incident one year ago in which the US government had video and other evidence of certain aspects of an actual attack by Syrian aircraft, which involved the use of sarin gas.
But they backed action in Iraq the following year, and again in Syria in 2015, strictly limiting strikes to Islamic State (IS) group targets.
France already has some 1,100 troops involved in its Operation Chammal, created in 2014 to fight Islamic State extremists in Iraq and extended in 2015 to Syria, as part of the US -led coalition. Multiple IS terror attacks have targeted France, including one last month.