"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.

Washington has promised a "forceful" response to an alleged chemical weapons attack on Saturday that killed at least 40 people in Douma, the last rebel outpost in the Syrian capital.

Russian Ambassador to the United Nations Vassily Nebenzia in turn has warned that US military action in Syria could lead to "grave repercussions."

The Russian foreign ministry on Wednesday furiously dismissed the allegations of use of chemical weapons, saying they were fabricated to bring about the ouster of Moscow ally President Bashar al-Assad.

"This is a total deception on a global scale," foreign ministry spokeswoman Maria Zakharova told journalists at a briefing.

"Damascus has neither the motive to use chemical weapons nor the chemical weapons themselves. There is no proof of their use by Damascus," she said.

"No one wants proof or facts. All the decisions have been taken, the aim as before is to remove Assad," she said.

Russia on Tuesday at the United Nations Security Council vetoed a US-drafted resolution on setting up a panel to identify the perpetrators of alleged toxic gas attacks in Douma.

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