Moscow said it would halt operations in Aleppo on Thursday for an eight-hour span between 08:00 (05:00 GMT) and 16:00, BBC wrote.
The Russian defence ministry said the pause was agreed so that civilians and rebels could leave the city.
But UN agencies say at least 12 hours will be needed for that to happen.
"We would welcome any pause in the fighting, but there is a need for a longer pause in order to get the aid in," said UN spokesman Stephane Dujarric.
Russia's announcement came on the day 14 members of one family were reportedly killed in a strike in Aleppo.
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Russian defence ministry official Sergei Rudskoy announced the pause in attacks on Monday afternoon.
"For that period, Russia's air force and Syrian government forces will halt air strikes and firing from other weapons."
Rudskoy said Russia was working towards a solution on Aleppo, but that "reaching an agreement on all issues may take a long time," according to the report.
"Therefore, we have taken a decision not to waste time and to introduce 'humanitarian pauses', mainly for the free passage of civilians, evacuation of the sick and wounded, and withdrawal of fighters," he said.
