Syrian rebels are willing to agree to a temporary truce as long as there are international guarantees that Damascus' allies Russia and Iran will stick to it.
The Higher Negotiations Committee will meet on Monday to discuss the proposed ceasefire after rebel representatives gave their "initial approval”, a statement from its chairman Riad Hijab said.
The government of Syrian President Bashar al-Assad was not itself in a position to sign off on a truce, as it was depending on Russian airstrikes and ground forces from pro-Iranian militias, the statement charged.
It quoted "sources inside the opposition factions" as saying that any agreement would have to go into effect simultaneously on all fronts.
It added that a ceasefire must also be accompanied by aid deliveries, the ending of all sieges and the release of prisoners.
A cessation of hostilities by Friday was proposed on February 12 by world powers meeting in Munich, Germany. Part of the plan was also to ensure access for humanitarian aid to besieged areas in Syria.
But there were ongoing clashes, shelling and air raids on Friday, and UN Syrian envoy Staffan de Mistura also said that it would not be possible to resume peace talks on February 25 as planned and that more work was needed to prepare for them.
Russian Foreign Minister Sergei Lavrov and US Secretary of State John Kerry discussed over telephone the problems in implementing a truce and the possibilities of military co-ordination, according to a statement from the Foreign Ministry in Moscow.
During the call Kerry also "restated his deep concern over the indiscriminate nature of continued bombing by Russian military aircraft and the lives being lost as a result", US State Department spokesman John Kirby said in a statement.
They also talked about the progress made in humanitarian aid deliveries to besieged areas of the country.