The move is intended to halt fighting and create a safe corridor for civilians trapped by the conflict.
The affected city has faced severe shortages of food, water, medicine and electricity after sustained attacks damaged essential infrastructure.
U.S. officials said the ceasefire would provide urgent relief and allow humanitarian agencies to assess conditions and deliver supplies.
The announcement comes as negotiations over a broader settlement remain uncertain, with Kyiv and Moscow continuing to disagree over territorial control and security guarantees.
Ukrainian officials have urged residents to remain cautious, warning that previous ceasefire efforts have collapsed amid renewed shelling.
International monitors are expected to track compliance, though access to the city remains limited and the situation on the ground is fluid.