Defense Secretary Jim Mattis, however, indicated that evidence of what happened was still being studied.
Syria's Foreign Ministry said Wednesday that Trump's threats to attack are "reckless" and endanger worldwide peace and security.
Macron said Thursday that France has proof that the Syrian government launched chlorine gas attacks and said France would not tolerate "regimes that think everything is permitted".
According to the sources, the specific response being considered in the event of US military action against Syria is Japan's "support for the USA resolve to fulfill its responsibility to prevent the use of chemical weapons".
During the two-hour meeting yesterday afternoon, ministers agreed to join forces with the USA and France to prevent Syrian leader Bashar al-Assad's forces from launching an "appalling and inhumane" attack again.
But after being criticized for apparently telegraphing USA intentions, Trump on Thursday attempted to blur the timing of any potential airstrikes on Syria.
US President Donald Trump had earlier warned regime-backer Russian Federation that "missiles will be coming" to Syria over the alleged attack in Douma that rescuers said killed 40 people. Trump notably did not rule out plans to attack Syria in retaliation for the weekend's suspected chemical attack on civilians at the hands of the Assad regime.
The U.S., France and Britain have been consulting about launching a military strike.
"There has been no decision to take military action at this point".
US, France, Britain launch strikes on Syria
Lebanon's Iran-backed militant group Hezbollah early in the day said that Israel had made a "historic blunder" using all the attack.
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"The chemical weapons attack that took place on Saturday in Douma in Syria was a shocking and barbaric act", May told reporters on Wednesday.
Syrian opposition activists and rescuers said poison gas was used on the rebel-held town near the capital, an allegation strongly denied by the Assad government. "Not to react is to prove to the rest of the world that what we say does not matter".
French President Emmanuel Macron claimed that the country had "proof" the Assad regime used chemical weapons in Douma and would support any USA action.
Moisi stressed the "risk of escalation" of the conflict amid increasing concerns about a U.S. -Russia proxy war.
Donald Trump, the USA president, has slammed Russian Federation for its partnership with "Gas Killing Animal" Bashar al-Assad, the Syrian president, spurring concerns that a United States strike could lead to a conflagration with Russian Federation, which has major military facilities at Tartus and Khmeimim and works cheek-by-jowl with Syria forces that could be targeted. May isn't legally required to do that, though it has become conventional since the 2003 invasion of Iraq for lawmakers to be given the chance to vote before British forces are deployed.
Corbyn has said any action in Syria should be put to a parliamentary vote.
It has been observed in subsequent military deployments in Libya and Iraq and many British lawmakers and voters are deeply sceptical of deepening involvement in the Syrian civil war.
The statement made no specific reference to military action. The Syrian government has been known to use chlorine bombs, along with sarin, a nerve agent developed by Nazi Germany that was used in a 2013 attack that killed almost 1,500 people outside of Damascus. France is already involved in the US -led coalition created in 2014 to fight the Islamic State group in Syria and Iraq. Multiple Islamic State retaliatory attacks have targeted French soil, including just last month.