Trump on Thursday also suggested he did not get enough credit for United States gains against ISIS in the region. US officials have been consulting with France, Britain and other allies on a possible joint military operation, but the timing remained in doubt Wednesday.
Amid speculation a US -led strike conducted with several allies on multiple Syrian targets could be imminent, Trump has publicly warned Russian Federation "missiles will be coming to Syria" before insisting on Twitter that he "never said when an attack on Syria would take place".
He said earlier this week that France was ready to attack the "chemical capabilities" of the Assad regime. Despite that warning, Trump tweeted: "Never said when an attack on Syria would take place".
Earlier, French President Emmanuel Macron said France had proof the Syrian government carried out the attack, which aid groups have said killed dozens of people, and will decide whether to strike back when all the necessary information has been gathered.
Amid the unprecedented tension between the two former Cold War adversaries, the Syrian Observatory for Human Rights said the Syrian government evacuated forces from a number of air bases around the country.
Fellow Tory MP Bob Seely - a member of the foreign affairs select committee - said Mrs May did not need parliamentary approval if the United Kingdom offered non-lethal support to the US. "I would like to note that the threat of using force against a United Nations member state is a gross violation of the charter of this organization", Russian Foreign Ministry spokeswoman Maria Zakharova said on Thursday.
"On a strategic level, it's how do we keep this from escalating out of control, if you get my drift on that", he said.
Moisi stressed the "risk of escalation" of the conflict amid increasing concerns about a U.S. -Russia proxy war.
Syria and its main ally, Russia, have denied that any chemical weapons were used and gave permission for the OPCW to investigate.
Following the alleged attack, an aide to Trump said Sunday that no response was "off the table" when it came to responding to the suspected incident.
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The Russian military, which has troops in Syria, said on Monday that its officers had visited the site of the alleged attack and found no evidence to back up reports of poison gas being used.
May isn't legally required to get Parliament's backing for military action, though it is conventional for lawmakers to be given the chance to vote.
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 US-led invasion of Iraq.
British Prime Minister Theresa May was set to hold a cabinet meeting Thursday to discuss possibly joining the United States and allies in military action, saying the weekend chemical attack on Douma "cannot go unchallenged".
He did not say whether France was planning military action.
Germany has deployed reconnaissance and refuelling flights as part of the worldwide operation against Islamic State of Iraq and the Levant (ISIL) in Syria.
"I think it is important to have a common line, without Germany participating militarily", Merkel said. "There is no real US policy on Syria". Multiple Islamic State retaliatory attacks have targeted French soil, including just last month.
In addition, a French frigate is stationed off of Lebanon in global waters.
Asked about possible USA strikes on Syria, President Vladimir Putin's spokesman Dmitry Peskov said that "it's necessary to avoid any steps that may fuel tensions in Syria".