Moscow's proposal to hold a "Congress of Syrian National Dialogue" on November 18 was announced on Tuesday at the end of the latest round of talks on Syria held in the Kazakh capital Astana.
Those talks have run in parallel to negotiations held in Geneva with the backing of the United Nations.
The Syrian National Coalition, an umbrella organisation of opposition groups in exile, "will not participate in any negotiations with the regime outside the framework of Geneva... and without the sponsorship of the United Nations," spokesman Ahmed Ramadan said.
On Tuesday, Russia's foreign ministry website listed 33 Syrian organisations invited to the planned congress in the Russian city of Sochi, including pro-regime forces and the full spectrum of opposition groups.
The proposal "is a joke in bad taste proposed by the regime in cooperation with Russia," said Yehya al-Aridi, a spokesman for the High Negotiations Committee, which represents key opposition groups at the Geneva talks.
"We have dozens of reasons to reject the Russian initiative. The main one is that it does not provide a solution to the Syrian crisis, it does not bring security to Syrians or rid them of a regime programmed to kill them," he added.
"Russia wants to impose opposition factions fabricated by the regime," he said, referring to parties created in Damascus after the conflict erupted in 2011 but which the opposition in exile sees as aligned with the regime.
| It does not provide a solution to the Syrian crisis, it does not bring security to Syrians or rid them of a regime programmed to kill them |
The head of the Syrian government's delegation to the Astana talks, Bashar al-Jaafari, said the regime "of course is ready to participate" in the Sochi conference, the official SANA news agency reported.
The Syrian conflict began when the Baath regime, in power since 1963 and led by President Bashar al-Assad, responded with military force to peaceful protests demanding democratic reforms during the Arab Spring wave of uprisings, triggering an armed rebellion fuelled by mass defections from the Syrian army.
According to independent monitors, hundreds of thousands of civilians have been killed in the war, mostly by the regime and its powerful allies, and millions have been displaced both inside and outside of Syria. The brutal tactics pursued mainly by the regime, which have included the use of chemical weapons, sieges, mass executions and torture against civilians have led to war crimes investigations.
Recent rounds of talks in Kazakhstan have focused on ironing out the details of a Russia-led plan establishing four "de-escalation" zones in Syria.
A new round of UN-backed Syria talks is scheduled to be held from November 28 in Geneva.