Negotiations between the opposition and rebel groups and Russia come as UN chief Antonio Guterres renews call for an "immediate cessation" to regime operations in Daraa province.
The Syrian opposition is in negotiations with the Russians about an agreement to restore regime control over southwestern Daraa province, opposition and rebel negotiators said on Saturday.
The regime's offensive this month in southwest Syria has taken much of the eastern part of Daraa province from the opposition and rebels, backed by a bombardment that the United Nations says has pushed 160,000 people out of their homes.
Opposition negotiators and a spokesman said a six-member civilian and military committee of the southern rebels held a preliminary meeting along the administrative borders of neighbouring Sweida province.
"The committee held its first meeting with Russian officers who presented their demands," said Ibrahim Jabawi, a spokesman of the central operations room set up by the main Free Syrian Army groups in southern Syria.
A second round of talks is expected on Saturday.
The deal being discussed does not include opposition and rebel territory in adjacent Quneitra province, bordering the Israeli-occupied Golan Heights, the spokesman said.
Jordan, which borders Deraa province, has been facilitating talks between rebel factions and Moscow over a deal that would end the violence in exchange for the return of state rule there.
UN chief renews call for ceasefire
UN Secretary-General Antonio Guterres issued a new call on Friday for "an immediate cessation" to regime's operations in rebel-held areas of Deraa.
Guterres is "deeply alarmed by the military offensive in southwestern Syria and its devastating toll on civilians," said a statement from his spokesman Stephane Dujarric.
"The secretary-general recalls that the southwest area of Syria is part of a de-escalation agreement agreed between Jordan, Russia and the United States," the statement said.
Guterres has called on "all parties to respect their obligations under international humanitarian law and human rights law, protect civilians and facilitate safe, unimpeded and sustained humanitarian access."
The UN chief made a similar call earlier this month after Russian-backed Syrian regime forces began attacking opposition-held parts of Daraa province on June 19.
More than 160,000 people have been forced to flee in southwestern Syria since Damascus launched an offensive to recover an area near the borders with Jordan and the Israeli-occupied Golan Heights, the Syrian Observatory for Human Rights said on Friday.
The war monitor says that nearly 100 civilians have been killed.
Unconfirmed reports of ceasefire
A Jordanian official source said on Friday there were confirmed reports of a ceasefire in southern Syria that would lead to "reconciliation" between opposition and regime's forces whose battles have stirred fears of a humanitarian catastrophe.
The source did not elaborate further on the reports.
Earlier government spokeswoman Jumana Ghunaimat told state news agency Petra that Jordan backed a "ceasefire and calm that would protect civilian lives, especially children and women."
However, a state department official in Washington said the United States could not confirm the truce report, and the situation in southern Syria remained "grim" with Russia and Syrian regime forces continuing to bomb the area.