Syrian rebels
Syrian rebelsReuters

Russia said Friday that only Moscow and the Syrian regime were fulfilling a truce deal hammered out with the United States, but stressed it is ready to extend it for another 72 hours.

"Although the ceasefire agreement is bilateral, only one side is truly implementing it," defende ministry spokesman Igor Konashenkov said in a />statement.

Konashenkov also slammed Washington for "unsuccessful" attempts at controlling US-backed rebels in Syria, which Moscow has accused of violating the ceasefire brokered by the two powers last week.

Despite accusing Washington and the rebels of not holding up their end of the deal, senior Russian officer Viktor Ponikhir announced in a televised briefing that Moscow was ready to extend a Syria truce set to run out Friday evening for a further 72 hours.

A ceasefire deal that went into force at sundown on Monday -- meant to end hostilities and ensure aid deliveries -- also calls for the demilitarization of the Castello Road, the main route for humanitarian assistance into the divided Syrian city of Aleppo.

Senior Russian officer Vladimir Savchenko said Friday that government troops have returned to the Castello Road after aborting a pullback because rebels were not withdrawing as agreed.

"Despite the agreement, opposition ranks have not withdrawn their hardware and weapons from the Castello Road," Savchenko said.

"As a result, with nightfall approaching, the weapons and military hardware withdrawn by government troops were returned to their previous positions."

UN Syria envoy Staffan de Mistura has warned that the aid could not move into Syria's second city before the Castello Road supply route had been fully secured.The UN Security Council will hold an urgent meeting at 2130 GMT on Friday to discuss the details of the US-Russian deal as it weighs whether to endorse the agreement.

Once aid is delivered and the ceasefire holds for seven days, the United States and Russia were due to begin coordinating military action against jihadist groups in the country.

Russia, which is flying a bombing campaign in support of the Syrian regime, is pushing for the Security Council to endorse the agreement, but France and other council members have said they first need to learn more details about the deal.