The Jordanian diplomat, Ayman Safadi, said he will head to Moscow on Tuesday and added that he was confident his meeting with Sergey Lavrov would produce more understandings and lead to "more steps forward to contain this crisis and prevent more destruction".
The Syrian government has repeatedly accused Israel of backing the rebels in southern Syria, including in Daraa, the nearby countryside of Sweida province and in the province of Quneitra near the Israeli-occupied Golan Heights.
But the observatory said Monday that some rebel groups accepted the proposal while others, mainly the al-Qaida-linked Nusra Front, otherwise known as the Levant Liberation Committee, has rejected the proposal.
The violence has displaced between 270,000 and 330,000 people, according to the United Nations, many south to the border with Jordan or west to near the Israeli-occupied Golan Heights.
Some 650,000 Syrian refugees have registered with the United Nations in Jordan since fleeing their country's seven-year war, which started with anti-government protests in 2011.
Accompanied by a major Russian aerial bombing campaign that has led to some of the fastest mass displacements of the war, Syrian pro-government forces have marched swiftly into insurgent territory in Deraa province over the past two weeks.
Shortly after the announcement, Syrian Observatory for Human Rights said Russian airstrikes had hit southwestern Syria for the first time in four days, hitting the opposition-held towns of Tafas and Saida.More news: Ohio State Investigators' Emails To Jim Jordan Went To Bad Address
Talks leading up to the agreement - which stipulates the opposition handing over heavy weaponry to the government - were mediated by neighbouring Jordan.
"Negotiations with the Russian enemy in Busra al-Sham have failed, after they insisted on the surrender of heavy weapons", it said in an online statement.
Diplomatic sources say that wider negotiations were hard, with Russian Federation insisting on sweeping surrender terms and rebels seeking an agreement that would make Jordan a guarantor of the safety of Deraa province's 800,000 civilians.
The strategic area was ostensibly protected by a ceasefire agreed by the US, Jordan, and Russian Federation just under a year ago, but President Al Assad is dead-set on retaking it.
Fierce battles were still ongoing around Daraa city, near the Jordanian border, where the army had repeatedly failed to capture a disused air base, rebels said.
Rebels and residents say a string of rebel towns have reached their own surrender arrangements that have allowed Russian military police to enter and patrol their towns.