A spokesman for the Russian government, Dmitry Peskof, said USA missiles should target "terrorists" and not the "legitimate government" in Syria.

Despite the 59 Tomahawk missiles the Trump administration unleashed on Shayrat airbase, the Assad regime nonetheless saw fit to carry out a chemical weapons attack of similar size and scale just last week.

Both Trump and his defence secretary Jim Mattis abruptly cancelled upcoming travel plans Tuesday, as the USS Donald Cook - a guided-missile destroyer - moved to within striking range of Syria.

Asked whether the USA military was ready to conduct an attack in Syria if ordered, Mattis replied, "We stand ready to provide military options if they're appropriate, as the president determines".

President Vladimir Putin's spokesman Dmitry Peskov said in televised remarks that "we don't participate in Twitter diplomacy".

In an earlier Wednesday tweet, Trump said that there was "So much Fake News about what is going on in the White House". A United States guided-missile destroyer, the USS Donald Cook, is in the Mediterranean.

Assad's Damascus regime, which has long accused Washington of supporting its armed opponents in the country's bloody seven-year-old civil war, hit back.

"We are not surprised by such a reckless escalation from a regime like the U.S. which has fostered and continues to foster terrorism in Syria", state news agency SANA quoted an official source at the foreign ministry as saying.

Syrian children stand in a basement used as a shelter against airstrikes on March 25, 2018, in Douma, eastern Ghouta on the outskirts of the capital Damascus.

A separate tweet says: "Be prepared, there is a small chance that our horrendous leadership could unknowingly lead us into World War III". "The continued use of chemical weapons can not go unchallenged".

The leader of the opposition Labour Party, Jeremy Corbyn, said however that the British parliament should be given a say on any military action.

They also congratulated the Syrian people, army and leadership on the great victories that were achieved, stressing that the final victory in the face of the terrorist war is imminent and that Syria will remain the home of moderate Islam in the face of extremist thought. The US Defense Department said it did not comment on potential military actions.

The World Health Organization said on Wednesday that 43 people had died in Saturday's attack on Douma from "symptoms consistent with exposure to highly toxic chemicals", and more than 500 in all had been treated.

Former President Barack Obama declared that the use of chemical weapons would be a red line that would prompt the United States' intervention. Worldwide inspectors are seeking clearance from Damascus to visit Douma under safe conditions to determine whether globally banned munitions were used, though they will not assign blame.

President Donald Trump's national security team has met to discuss the USA response to the Syrian government's apparent use of chemical weapons on its own people.

French President Emmanuel Macron, who has been coordinating closely with Washington, is to decide on a response in the coming days, having insisted he does "not want an escalation" and that any response would focus on Syria's chemical capabilities, not on allies of the regime. Wednesday's statement is also notable because Trump has criticized his predecessors for publicly telegraphing United States military action. Social media pages were flush with defiant comments, mostly from government supporters, some lamenting Syria's perpetual conflict while others taunted Trump to go through with his threats.

The Eurocontrol airspace organization said that the European Aviation Safety Agency had sent a "Rapid Alert Notification" that flight operators needed to consider the possibility of air or missile strikes on Syria.