The leader of the Western-backed rebel Free Syrian Army has said that forces aligned to him will not join the peace conference in Geneva in January.
Gen Salim Idris, head of the FSA's Supreme Military Council, told al-Jazeera that they would continue to try to topple President Bashar al-Assad.
He warned Mr Assad would use the talks to buy time and continue to wage war.
Iran, which is closely allied to the Syrian government, said it would attend if it was invited.