Hundreds of people have been killed in nearly two weeks of conflict between the army and a rival paramilitary force - the Rapid Support Forces (RSF) - which are locked in a power struggle that threatens to destabilise the wider region.
An RSF statement accused the army of attacking its forces on Thursday and spreading "false rumours", making no reference to the proposal which the army said came from the Intergovernmental Authority on Development (IGAD), an African regional bloc.
Gunfire could be heard on Thursday in the Khartoum area, a resident told Reuters.
The existing three-day ceasefire brought about a lull in fighting, without completely halting it, but was due to expire at midnight (2200 GMT) and many foreign nationals remained trapped in the country despite an exodus over the past few days.
The army late on Wednesday said its leader, General Abdel Fattah al-Burhan, had given initial approval to the plan to extend the truce for another 72 hours and to send an army envoy to the South Sudan capital, Juba, for talks.
The military said the presidents of South Sudan, Kenya and Djibouti worked on a proposal that includes extending the truce and talks between the two forces.
"Burhan thanked the IGAD and expressed an initial approval to that," the army statement said.
Reuters could not immediately reach an IGAD spokesperson for comment.
US Secretary of State Antony Blinken and African Union Commission Chairperson Moussa Faki Mahamat discussed working together to create a sustainable end to the fighting, the State Department said in a statement on Wednesday.
At least 512 people have been killed and close to 4,200 wounded since by the fighting since April 15.
The crisis has sent growing numbers of refugees across Sudan's borders. The U.N. refugee agency has estimated 270,000 people could flee into South Sudan and Chad alone.
With air strikes and artillery unleashed during the fighting, the conflict has destroyed hospitals and limited food distribution in the vast nation where a third of the 46 million people were already reliant on humanitarian aid.
An estimated 50,000 acutely malnourished children have had treatment disrupted due to the conflict, and those hospitals still functioning are facing shortages of medical supplies, power and water, according to a U.N. update on Wednesday.
Deadly clashes broke out in Geneina in West Darfur on Tuesday and Wednesday resulting in looting and civilian deaths and raising concerns about an escalation of ethnic tensions, the update said.
France said on Thursday it had evacuated more people from Sudan, including not only French nationals but also Britons, Americans, Canadians, Ethiopians, Dutch, Italians and Swedes - part of a wider exodus of expatriates.
Foreigners evacuated from Khartoum have described bodies littering streets, buildings on fire, residential areas turned into battlefields and youths roaming with large knives.
Tension had been building for months between Sudan's army and the paramilitary Rapid Support Forces (RSF), which together toppled a civilian government in an October 2021 coup.
The friction was brought to a head by an internationally-backed plan to launch a new transition towards elections and a government led by civilian parties.
A final deal was due to be signed earlier in April, on the fourth anniversary of the overthrow of long-ruling Islamist autocrat Omar al-Bashir in a popular uprising.
