Sudan's military ruled out negotiations with a rival paramilitary force on Thursday, saying it would only accept its surrender as the two sides continued to battle in central Khartoum and other parts of the country, threatening to wreck the latest attempt at a ceasefire.

The military's statement raised the likelihood of a renewed surge in the nearly week-long violence that has pushed Sudan's population to the breaking point.

The alarm has grown that the country's medical system was on the verge of collapse, with many hospitals forced to shut down and others running out of supplies.

The 24-hour ceasefire, declared on Wednesday evening, had brought only marginal calm to parts of the capital of Khartoum, but many residents took advantage to flee the homes where they have been trapped for days.

“Massive numbers” of people, mostly women and children, were leaving in search of safer areas, said Atiya Abdulla Atiya, secretary of the Doctors' Syndicate.

Hours before the truce was set to end, the military said in a statement that it would not negotiate with its rival, the Rapid Support Forces, over an end to the crisis and would only discuss terms of its surrender.

“There would be no armed forces outside (of) the military system,” it said.

If the truce collapses completely, it would mark the second failure by the international community to push Sudan's two top generals — army chief General Abdel Fattah Burhan and RSF commander General Mohammed Hamdan Dagalo — to halt their battle for control of the country.

A similar truce on Tuesday, which came after US secretary of state Antony Blinken spoke by phone with both generals, collapsed almost immediately.

Diplomatic efforts had been on to salvage to the latest attempt. On Thursday, Turkish President Recep Tayyip Erdogan spoke with the two generals as well, urging a return to dialogue.

The leaders of Egypt, which is allied to Sudan's military, and of the UAE, which is linked to the RSF, also spoke on Thursday on how to turn the ceasefire into negotiations.

At least 330 people have been killed and 3,300 wounded in the fighting since it began on Saturday, the UN's World Health Organisation said, but the toll is likely higher because many bodies lie uncollected in the streets.