It is at least the third ceasefire to be announced since violence erupted this month but none have held.
Mr Blinken said agreement had been reached between the army and the paramilitary Rapid Support Forces (RSF) after 48 hours of negotiations.
BBC reports at least 400 people have been killed since fighting erupted on 15 April.
UN Secretary General António Guterres has warned the violence in Sudan risks causing a "catastrophic conflagration" that could engulf the whole region and beyond.
