There was no immediate response from President Bashar al Assad's opponents, whose attendance at the talks in Switzerland remained in doubt - prompting a last-minute appeal to them from the US.
Syrian Foreign Minister Walid al-Moualem, on a visit to Moscow, said he had given Russian officials a plan for a truce in Aleppo, Syria's biggest city, and said the government was ready to exchange lists of prisoners to be swapped.
Moscow and Washington, which favour opposing sides - respectively for and against Assad - have urged both parties to make concessions including ceasefires, access for aid and prisoner exchanges to build confidence before the conference.
But there is little sign of coherent negotiating positions or of violence abating. Rebels are fighting each other, in battles involving Islamist militants whose influence has cooled Western support for the uprising. Mr Assad's forces, once reeling, have recovered and reportedly been bolstered by new Russian arms and supplies.
Most of the disparate rebel forces fighting inside Syria have dismissed the negotiations, known as Geneva-2, and opposition leaders backed by Western and Arab powers met in Turkey to decide whether to take part. It remained unclear when they would reach a final decision.
The United States, the co-sponsor of the talks with Russia, issued an 11th-hour appeal to Mr Assad's opponents to participate in the first direct peace negotiations in nearly three years, to end a civil war that has killed more than 100,000, driven millions from their homes and inflamed tensions across the region and beyond.
The Syrian National Coalition, a fractious 120-member body, has already seen some of its members declare their hostility to joining the talks at Montreux - many fearing it will undermine their credibility at home to engage in a process they see as having little chance of forcing Mr Assad to step down.
"The United States ... urges a positive vote," US Secretary of State John Kerry said on Thursday.
"The Geneva peace conference is not the end but rather the beginning, the launch of a process ... that is the best opportunity for the opposition to achieve the goals of the Syrian people and the revolution."
Mr Kerry also poured scorn on "revisionism" from Damascus, which has made clear it rejects rebel and Western demands that Mr Assad make way for a transitional leadership and has suggested talks focus on cooperation against "terrorism" - code for the Islamists, including al Qaeda, that dominate on the front lines.
"Syria ... is the strongest magnet for terror of any place today," Mr Kerry said. "It defies logic to imagine that those whose brutality created this magnet ... could ever lead Syria away from extremism and towards a better future."
Russian Foreign Minister Sergei Lavrov said of the opposition's delay in agreeing to take part: "It worries us very much that some kind of game is being played."
Mr Lavrov called again for Tehran, Mr Assad's main sponsor in the region, to be represented at the conference - something other powers have resisted on the grounds that Iran has not endorsed the view that an interim administration should be established to end the conflict.