"We do not take part in Twitter-diplomacy. We support serious approaches. As ever, we believe it is important not to take steps that could damage an already fragile situation," presidential spokesman Dmitry Peskov said in comments reported by news agencies.

Trump tweeted that strikes could be expected in retaliation for an alleged chemical weapons attack on civilians in Syria's Douma, telling regime-backer Russia to "get ready".

The message comes one day after Russia vetoed a US-drafted resolution at the UN Security Council to set up a panel to identify the perpetrators of Saturdays' alleged toxic gas attacks.

Russia has said its military specialists found no evidence of a chemical attack, and suggested that rebels staged or spread rumors of an attack to pin the blame on Damascus.