An Aleppo representative for the Free Syrian Army (FSA) rebel group, however, effectively rejected the freeze, setting virtually impossible-to-achieve conditions.
"My meetings here with the government and with President (Bashar al-) Assad gave me the feeling that they are studying very seriously and very actively the UN proposal," De Mistura said at a press conference in Damascus.
"The initial response by the government of Syria... Was of interest and constructive interest," he added.
Yesterday, Assad said he was ready to study the UN plan to "freeze" fighting in Aleppo, which has been divided into government- and rebel-held areas since an insurgent offensive in mid-2012.
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De Mistura put the so-called "action plan" forward last month to allow for aid deliveries and to lay the groundwork for peace talks, saying Aleppo would be a "good candidate" for such a freeze.
"All Syrians need a concrete example... That's why we have come to the conclusion of making a specific proposal," he said.
In recent months, government forces have advanced around the outskirts of the eastern portion of the city that is under rebel control, threatening to encircle it completely.
De Mistura stressed that the "freeze" proposal was an "action plan, not a peace plan yet."
"Certainly this is not a substitute for a political solution, but it is an incentive in that direction."
Rebel-held areas of Aleppo are under the control of multiple groups, including fighters affiliated with the Western-backed FSA.