Syrian President Bashar al-Assad confirmed to his Russian counterpart Vladimir Putin that Syria is ready to help implement a cease-fire planned to begin on Saturday.
The two leaders spoke by telephone Wednesday and highlighted the importance of continuing to fight terror groups such as Islamic State and Jabhat al-Nusra. The militants are not part of a U.S.-Russian proposal for a cessation of hostilities.
Other groups are supposed to say by Friday whether they are taking part.
The main opposition High Negotiations Committee has said its participation is contingent on the delivery of humanitarian aid and the end of sieges and airstrikes against civilians.
Russia's Interfax news agency quoted Foreign Ministry spokesman Dmitry Peskov saying the cease-fire is the government's main focus in Syria and that it is premature to talk about any backup plan.