On Thursday, Trump also pushed back against a New York Times report that he "sought to fire" special counsel Robert S. Mueller, who is leading the federal investigation into Russian meddling in the 2016 presidential election. Donald Trump tweeted, "Get ready Russia because the missiles are coming nice, new and smart".
The Russian military said later it had observed movements of US naval forces in the Gulf.
He said he is confident that "no one wants a war", but added that "such incidents could result in a huge disaster in the current tense environment".
"Meetings are ongoing, important decisions are being weighed even as we speak", she said.
Wednesday's tweet was the second time since the Syrian chemical attacks were first reported that Trump has called Assad an "animal", and spoken tenuously about his administration's very complicated relationship with Russia.
"The continued use of chemical weapons cannot go unchallenged".
The perpetrators of Monday's attack on the airbase are also unknown, but the Russian Defense Ministry and Syria have accused Israel of carrying out the bombings.
Trump said Wednesday 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!'" His Russian and Iranian backers will ensure that.
This led Mr Trump to take to social media, tweeting: "Russia vows to shoot down any and all missiles fired at Syria".
Would U.S. allies join in the fight?"We're still working on this".
But the Russian army continued to deny their side's latest victory came after Assad launched a chemical attack on the last rebel-held pocket of the enclave in the Damascus suburbs, instead accusing the White Helmets civil defense organization of staging the massacre.
The Syrian conflict has increasingly widened the rifts between Moscow, Washington and European powers and inflamed the bitter rivalries that run across West Asia. Like the assassination of Archduke Franz Ferdninand that preceded World War I, the potential missteps in dealing with the Syrian crisis could be the launching point of World War 3.
More than 40 Syrians, including men, women and children, choked to death after a suspected chemical attack in the city of Douma on Saturday. "We have the proof that chemical weapons - at least chlorine gas - were used by Assad's regime", Macron told France's TF1 television.
Families were reportedly found suffocated in their homes and shelters, with foam on their mouths.
Russia and Syria quickly responded to Trump's threat on Wednesday.
By inviting the international chemical weapons watchdog to send a fact-finding mission to Syria, the government claimed it proved it was innocent of the allegations of using chemical weapons.
That assault prompted the US to launch several dozen Tomahawk cruise missiles at a Syrian air base.