"As before we would hope that all sides will avoid steps that in reality are not provoked by anything and that could destabilise the already fragile situation in the region," Kremlin spokesman Dmitry Peskov told journalists.

"The situation is tense," Peskov said, adding that Russia is calling for an "unprejudiced and objective investigation before making judgements" on the suspected use of chemical weapons.

Russia on Tuesday at the United Nations Security Council vetoed a US-drafted resolution on setting up a panel to identify the perpetrators of toxic gas attacks after chemical weapons were allegedly used in the rebel-held town of Douma.

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