A proposed United Nations resolution on a chemical weapons attack in Syria is "unacceptable" for Moscow, Russia's foreign ministry spokeswoman Maria Zakharova was quoted by Interfax news agency as saying on Wednesday.

"We do not believe it is expedient to pass a resolution on the chemical weapons attack in its present form," she added.

Washington, Paris and London have drawn up a draft U.N. Security Council statement condemning the attack and demanding an investigation. Russia has the power to veto it, as it has done to block all previous resolutions that would harm Assad.

Russia has already suggested it would publicly stand by Syrian President Bashar al-Assad and says the chemical incident which killed scores of people was likely caused by a leak from a depot controlled by Syrian rebels.