Magne Barth, head of the ICRC delegation in Syria, said more than 100 civilians were recently killed, some in densely populated areas of the city.
"The ICRC calls on the parties to the conflict in Aleppo and elsewhere in Syria to take constant care to protect and spare civilians," the organization said in a statement. "Parties must respect their obligations under international humanitarian law and take all feasible precautions to avoid civilian injuries and loss of life."
Several members of the ICRC and Syrian Red Crescent Society have been killed during the Syrian civil war since early 2011.
The Syrian Observatory for Human Rights, which has headquarters in London, said in reports earlier this week the Syrian air force conducted a major assault on Aleppo.
The observatory's counterpart, the Syrian Network for Human Rights, said Syrian military helicopters dropped steel barrels filled with oil and explosives on Aleppo in an assault it said constituted a war crime.