"Smart rockets should be aimed at terrorists, rather than the legitimate government, which has for several years been fighting international terrorism on its territory," foreign ministry spokeswoman Maria Zakharova said in a Facebook post.

Trump earlier warned in a tweet that regime-backer Russia should "get ready" for missiles, "because they will be coming, nice and new and 'smart'".

Zakharova also suggested the strikes could be a pretext to destroy evidence of an alleged chemical weapons attack in Douma, which Moscow has said was a staged "provocation" to justify Western intervention.

"Is the whole idea to quickly remove the traces of the provocation...(so) international inspectors will have nothing to look for in terms of evidence?" she asked.

Moscow has warned the US of the possible consequences of any use of force against the Syrian regime, "especially if this affects the Russian military", a source in the foreign ministry told AFP Wednesday.

"Russia will do whatever is necessary to defend its citizens on Syrian territory," the source said.