The military statement came hours before a ceasefire covering the city and its surrounds was set to expire.
But despite efforts to end the violence, fighting has continued between the military and rebel groups outside the city.
Aleppo has witnessed a flare-up in fighting in recent weeks, despite a nationwide agreement among many participants to cease hostilities.
Now Syria's military says it is extending a ceasefire in the city of Aleppo and its rural areas for 48 hours starting after midnight in Syria on Tuesday.
It comes as the United States says a new agreement with Russia will replace localised ceasefires in Syria with a revived, nationwide truce.
US Secretary of State John Kerry says it's hoped the agreement is a first step towards getting faltering peace talks back on track.
"These are words on a piece of paper, they are not actions but they are a commitment by Russia to in fact limit the Syrian regime from its ability to fly in civilian-occupied areas as well as to work with the commanders on the ground in order to try to deliver stability and a reaffirmation of the cessation of hostilities."
Russia and the United States issued a joint statement promising to step up efforts to persuade the warring parties to abide by the ceasefire agreement.
The statement said Russia would work with Syrian authorities "to minimise aviation operations over areas that are predominantly inhabited by civilians or parties to the cessation".
It also said the US and Russia would press parties to the conflict to allow humanitarian deliveries to several towns which have been largely cut off by the fighting.
US State Department spokeswoman Elizabeth Trudeau says both the US and Russia have been in touch with local commanders.
"These small, short-term cessation of hostilities were a means to get local commanders to be assured of the other sides readiness to renew the implementation of cessation. With our statement today, we do believe that the cessation is in place. We do believe that this was a confidence-building measure, that this cessation, then, will be across (the country). We're not ruling out, you know, scattered violence. We're not ruling out that there could be attacks either way, but we do believe that this is now in place."
France's Foreign Affairs Minister, Jean-Marc Aryault, also welcomed the agreement.
"Our common objective is that this statement is implemented: it can't just be another declaration; and that it be respected by all and, once more, as quickly as possible."
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