The US and Russia say they want to extend the ceasefire they have brokered in Syria.
But the truce looks shaky, undermined by increasing violence and a failure to deliver aid.
Moscow says UN Security Council backing looks unlikely because the US does not want to share documents about the agreement with the body.
A closed door briefing to the Council was cancelled on Friday at the last minute.
“We are ready to extend the ceasefire for another 72 hours,” said Viktor Ponzikhir, Deputy Head, Russian General Staff’s Main Operations Command.
“We are expecting from the American side decisive actions aimed at influencing armed groups under its control in order for them to strictly abide by the September 9 agreement. Otherwise the situation in Syria can get out of control.”
The main dispute of the truce so far is over aid for Aleppo.
Pro-government forces encircled the rebel zone this month, trapping civilians there – with no way to bring in food.
The White House said on Friday that it was deeply concerned that the government continues to block the flow of humanitarian help, despite a decrease in violence following the truce.