With a mix of fear and defiance, Syrians braced on Wednesday for a possible U.S. attack in retaliation to an alleged chemical assault that killed dozens over the weekend.

U.S. President Donald Trump said Wednesday in a tweet that missiles "will be coming" in response to Syria's suspected chemical attack, adding "Get ready Russia, because they will be coming, nice and new and 'smart!'"

The statement was the latest in a war of words raging between Washington and Moscow since Saturday's attack on the opposition-held town Douma, just outside Damascus, which killed more than 40 people and affected 500 others according to activists and first responders. The Assad regime and its ally Russia deny such an attack happened.

So far, France, United Kingdom and Saudi Arabia have voiced support for a possible military operation in Syria, backing Trump's rhetoric.

The United States, Britain and France have argued the incident bears all the hallmarks of a strike ordered by the regime, which has been blamed for previous attacks by the Organisation for the Prohibition of Chemical Weapons (OPCW).

French President Emmanuel Macron, who has been coordinating closely with Washington, said he would decide on a response "in the coming days."

"Our decision will not target allies of the regime or attack anyone but rather attack the regime's chemical capabilities," he said, insisting he did "not want an escalation."

British Prime Minister told reporters on Wednesday that "the use of chemical weapons cannot go unchallenged."

BBC reported later on Wednesday that May was ready to confirm military intervention into Syria and no parliamentary approval would be required, whil the Daily Telegraph said that the prime minister ordered British submarines to move within missile range of Syria in readiness for strikes against Assad regime forces that could begin as early as Thursday night.

Meanwhile, Crown Prince Mohammed bin Salman of Saudi Arabia said during a joint news conference with the French President Macron that Saudi Arabia would support a military operation in Syria.

"If required by our alliance with our partners, we will be there," he said, according to the French translation of his remarks spoken in Arabic.