Syria offered rebels concessions, including a prisoner exchange, ahead of peace talks in Switzerland next week as the fractured opposition sought to get their own stalled negotiations underway Saturday on whether to attend.
Syrian Foreign Minister Walid Muallem, in Moscow for discussions with his Russian counterpart Friday, also raised hopes of a ceasefire in Aleppo, presenting Sergei Lavrov with a "security" plan for the devastated northern city.
Muallem said the Syrian regime was willing to swap prisoners with the rebels in the first such mass exchange since the conflict began in 2011 while Lavrov said Damascus was ready to take "a series of humanitarian steps" in the civil war.
Muallem said Syria would "make every effort to ensure Geneva II is a success and meets the aspirations of the Syrian people and the direct orders of President Bashar al-Assad".
He added that he had handed over "a plan concerning measures for ensuring security in Aleppo", after Russia and the United States this week issued a joint call for ceasefires in parts of the battle-scarred country.
But US Secretary of State John Kerry warned the regime that it would fail to divert the peace talks in Geneva away from the aim of installing a new government, saying "nobody is going to be fooled".
He accused Assad of funding and even ceding territory to extremist groups in order to fuel fears of militant groups.
Friday's proposals came as a divided opposition failed to formally open talks in Istanbul on whether to join the so-called Geneva II peace conference.
Kerry had appealed Thursday to the umbrella National Coalition not to boycott the Geneva talks and has sought to ally its fears that the negotiations would somehow legitimise Assad's regime and leave him in power.
The opposition National Coalition is under intense pressure from Western and Arab allies to turn up, with media reports suggesting the United States and Britain had threatened to withdraw support if it fails to send a delegation.
But parts of the opposition are wary of being drawn into a process they fear could result in Assad clinging to power.
"It is likely in the end that the coalition will send a delegation to Geneva but at what cost to its future," said one Western diplomat.
The much-delayed Geneva II conference is aimed at finding a way out of almost three years of brutal conflict that has claimed the lives of 130,000 people and forced millions from their homes.
National Coalition talks had originally been due to get underway on Friday but were postponed due to problems posed by some delegates, Coalition spokesman Khaled Saleh said.
The same delegates had threatened to resign at the last meeting of the Coalition 10 days earlier, concerned at the "lack of transparency" in the re-election this month of Ahmad Jarba as National Coalition leader.
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After lengthy haggling, the talks were rescheduled to begin on Saturday in a hotel in an Istanbul suburb, a western diplomatic source said.
More than 35 countries will gather in the Swiss cities of Montreux and Geneva from Wednesday for talks on setting up a transitional government to lead the country, in line with a 2012 deal.
But recent government advances have put the rebels at a disadvantage in any negotiations.
Opposition forces are increasingly riven by rivalries between Al-Qaeda-linked jihadists and more mainstream Islamists, with fierce battles that monitors say have killed more than 1,000 people in two weeks alone.
Jihadists on Friday withdrew from Saraqeb, their last bastion in the Syrian province of Idlib, five days into a major battle in the town against local rebels, a monitor said.
In the region of Aleppo, rebels also made advances except in Jarabulos on the border with Turkey, which the Islamic State of Iraq and the Levant (ISIL) seized, the Syrian Observatory for Human Rights said.
The fighting also spilled across the Lebanese border, with eight people, including five children, killed when shells fired from Syria rained down on the border town of Arsal on Friday, officials said.
After news of the deaths broke, violence erupted in the northern city of Tripoli, a frequent scene of Syria-related clashes and killings.
Turkey and Qatar held parallel talks in Ankara with four Syrian rebel groups, including the Islamic Front, the country's biggest rebel alliance, seeking to convince them not to oppose or participate in the Geneva II talks, a western diplomatic source said.
At the Istanbul talks the Coalition reiterated the stance of the moderate opposition to the Geneva II talks.
"The Coalition want to participate in a political solution to the Syrian conflict," said Saleh.
The objective is to put in place a transition government in which Assad will play no part, he added.
UN refugee chief Antonio Guterres, meanwhile, said it was vital to find a political solution to the conflict and end the suffering of Syrians.
And he pleaded for the world to ease the massive burden on countries which have taken in millions of refugees, after the UN earlier this week launched a massive $6.5 billion appeal for aid.
"What Syrian people need is peace and the possibility to go back to their country and to rebuild their country," he said at a meeting of refugee-hosting countries in Turkey.