"The proposal of (Russian Foreign Minister Sergei) Lavrov is a political manoeuvre and is part of useless procrastination that will only result in more deaths and destruction for the Syrian people," said an opposition statement published late Monday.
Meanwhile, China has welcomed the plan.
"We welcome and support the Russian side's suggestion," foreign ministry spokesman Hong Lei told reporters at a regular briefing in Beijing on Tuesday.
"As long as the suggestion is conducive to easing the current tension in Syria, solving the Syria issue politically and safeguarding peace and stability of Syria and the region, the international community should give positive consideration to it," he added.
Washington accuses Bashar al-Assad's forces of using chemical weapons to kill 1429 people last month, and has been looking to build international momentum for a punitive strike.
Russia's Foreign Minister Sergei Lavrov called on Damascus to "place the chemical weapons under international control and then have them destroyed".
President Barack Obama has said the idea could be a "significant breakthrough".
China is a veto-wielding permanent member of the United Nations Security Council, and over the course of the conflict it has joined with Russia, a fellow veto-holder, to block resolutions supported by Washington and its allies.
Beijing regularly calls for a "political solution" to the crisis in Syria.
