Syria's main Western-backed opposition coalition is expected to vote in Istanbul Saturday on whether to attend next week's peace talks in Geneva.
The Syrian National Coalition is under heavy U.S. pressure to attend the conference, which is aimed at forming a transitional government.
Opposition leaders so far have refused to attend talks without a prior commitment that President Bashar al-Assad will step down.
Meanwhile, Syria's government says it has given Russia a plan for a cease-fire in the country's largest city of Aleppo and an exchange of prisoners with Syrian rebels.
Syrian Foreign Minister Walid al-Moallem said during his visit to Moscow Friday he had turned over the proposals in preparation for peace talks with the rebels.
U.S. Secretary of State John Kerry warned the Syrian president Friday the U.S. is not out of options to pressure his government to comply with the goals set in the first Geneva conference.
The Syrian government considers all rebel forces to be terrorists, and has tried to shift the focus of the proposed peace talks from forming a new government to fighting extremism.
Kerry has said the talks are the "best opportunity for the opposition to achieve the goals of the Syrian people and the revolution."
The fighting is raging in Syria's northwest, with the conflict spilling over into Lebanon. Rocket fire in Lebanese border towns killed seven people on Friday.
Speaking after a trip to a Syrian refugee camp in Iraq, United Nations Secretary-General Ban Ki-moon told the U.N. General Assembly Friday the Syrian people need peace and depend on the U.N.'s solidarity for survival.
He said the U.N. is "intensifying efforts" to bring the parties together in Geneva next week and is pressing for the sides to move to a transitional governing body to stop the violence.