"The proposal of 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 a statement from the opposition Syrian National Coalition late Monday.
The Coalition added that "the violation of international law requires an appropriate international response" -- an indirect call to the administration of Barack Obama not to abandon the possibility of military strikes against Damascus.
Obama called Lavrov's plan a "significant breakthrough," and US Secretary of State John Kerry said that the move could stop possible military action against Syria.
US lawmakers are due to vote on a resolution authorising the use of force against the Assad regime in retaliation for alleged chemical attacks launched near the capital on August 21 in which hundreds are said to have died.
"The perpetrators of war crimes cannot be exonerated and crimes against humanity cannot be washed away by offering political concessions or by handing over the instrument used to commit the crimes," the opposition said, referring to the chemical weapons.
The rebel Free Syrian Army chief of staff Selim Idriss on Monday accused the regime of President Bashar al-Assad and his allies in Russia of lying, after Damascus said it welcomed the proposal.
"We call for strikes and we warn the international community that this regime tells lies, and the liar Putin is its teacher," Idriss told Al-Jazeera television.