Russia, the main backer of Syria's President Bashar al-Assad, has opposed a French-drafted resolution and was expected to propose a weaker Security Council statement on the chemical arms crisis, diplomats said.
A resolution is legally binding and if passed under Chapter VII of the UN Charter can include the use of military force. A council statement is largely symbolic.
The 15-member council was to start closed consultations at 2000 GMT, the council president announced.
Russia's foreign ministry said, however, that it would be "unacceptable" for the council to pass a resolution which blames the Assad government for an August 21 chemical weapons attack near Damascus which sparked a western threat of military strikes against government forces.
The United States, Britain and France accuse the Assad government of staging the attack, which the US administrations says killed more than 1,400 people. The government has blamed opposition rebels.