Russia's foreign minister Sergei Lavrov has said that the US decision to recognise the Syrian opposition coalition contradicts an agreement reached in Geneva in June to seek political transition in Syria.
Mr Lavrov said it appeared that the US had "placed all bets on the armed victory" of the Syrian opposition over the government forces.
Britain will seek to rally greater international support behind Syria's opposition today in an effort to increase the pressure on Bashar Assad's regime.
Foreign Secretary William Hague is joining representatives in Morocco of the more than 130 countries and global bodies that make up the Friends of Syria grouping.
Barack Obama has declared Syria's main opposition group the sole "legitimate representative" of its country's people, deeming the move "a big step" in the international diplomatic efforts to end Syrian president Bashar Assad's regime.
Mr Obama told ABC News that the newly formed Syrian Opposition Council "is now inclusive enough" to be granted the elevated status, which paves the way for greater US and international support for the organisation.