"If there is a US strike... the missiles will be downed as well as the sources they were fired from," Russian Ambassador to Lebanon Alexander Zasypkin said late Tuesday.

He made the comments on Al-Manar, a Lebanon-based television channel run by the Iran-backed Hezbollah movement, another key military ally of Syrian President Bashar al-Assad's regime.

The envoy argued the accusations that Damascus dropped chemical munitions on a rebel-held town in Eastern Ghouta last week were fabricated to justify strikes and added that Russia had long warned of the scenario.

Russian officials have repeatedly claimed in recent weeks that Syrian rebels, with support from the West, had been faking -- and training civilians to fake -- the symptoms of a chemical attack.

US President Donald Trump swiftly responded on social media.

"Russia vows to shoot down any and all missiles fired at Syria. Get ready Russia, because they will be coming, nice and new and 'smart!' You shouldn't be partners with a Gas Killing Animal who kills his people and enjoys it!" he wrote.

Trump and other Western leaders have vowed a quick and forceful response to Saturday's alleged chemical attack, which rescue workers say killed more than 40 people.