DONALD Trump has told Russia to "get ready" for American "smart" missiles heading to Syria while blasting Putin for partnering with "Gas Killing Animal" Bashar Assad.

The US President issued the extraordinary threat on Twitter following comments from senior Russian officials that Vladimir Putin's military would strike US bomb sites in retaliation to American aggression.

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How America and Britain could wage war against Syria and its major ally Russia

Trump tweeted: "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!"

The Republican firebrand then added: "Our relationship with Russia is worse now than it has ever been, and that includes the Cold War.

"There is no reason for this. Russia needs us to help with their economy, something that would be very easy to do, and we need all nations to work together. Stop the arms race?

Responding to Trump's tweet, a Russian foreign ministry spokeswoman said: "Smart missiles should fly towards terrorists, not a legal government."

The spokeswoman also reportedly said that US "smart missiles" could be an attempt to destroy evidence of an alleged chemical attack on the ground.