Sudan's military ruler has visited army bases near to the capital on his first trip away from Khartoum since an internal conflict broke out in April, as the United Nations warned that the war could tip the entire region into a humanitarian catastrophe.

General Abdel Fattah al-Burhan also intends to leave Sudan for talks in neighboring countries after visiting regional bases and Port Sudan, the temporary government seat, two government sources said.

Burhan, who is also armed forces chief, plans to chair a cabinet meeting.

The army has been fighting the paramilitary Rapid Support Forces (RSF) for control of Khartoum and several cities since April 15.

Burhan emerged on Thursday from the army headquarters, which the RSF says it has blockaded, and was seen in video and photos in the city of Omdurman, across the Nile.

The army circulated videos on Friday of Burhan visiting the Atbara artillery base, north of Khartoum in River Nile state. Burhan could be seen carried by cheering soldiers.

While the army has fought the RSF in Khartoum and the Kordofan and Darfur regions to the west, the central, northern, and eastern regions of the country have remained calm and under army control.

Attempts to mediate have proven fruitless as diplomats say both sides still believe they can win. More than 4-million people have fled their homes, basic services have collapsed, and the fighting has given way to ethnic attacks by the RSF and allied militias in Darfur.

"This viral conflict and the hunger, disease and displacement left in its wake now threatens to consume the entire country," United Nations aid chief Martin Griffiths said in a statement on Friday.

He said he was concerned about the expansion of fighting in the country's breadbasket Gezira state, just south of Khartoum where the RSF has made incursions.

"Hundreds of thousands of children are severely malnourished and at imminent risk of death if left untreated," said Griffiths, adding that diseases such as measles, malaria, dengue fever, and acute watery diarrhea were spreading.

A UN children's fund spokesperson said he expected a lack of supplies to lead to a spike in child deaths. MSF's Susanna Borges, who returned to Geneva from the Chad border this week, told reporters refugees had not received food rations in August and inadequate water supplies had prompted some to dig holes.

The $2.6-billion Sudan appeal is just 26% funded, according to a UN spokesperson at a Geneva briefing, calling on donors to speed up on promised aid.