The RSF, at war with the army since April 2023, appears to be preparing for an offensive to seize the army-controlled city, less than two weeks after it captured the city of El-Fasher -- the last army stronghold in the western Darfur region.

"The air defence system today shot down a drone launched by the RSF militia towards the city," said the military source, who requested anonymity because they are not authorised to brief the media.

El-Obeid, the capital of North Kordofan state, sits on a key supply route linking the Sudanese capital Khartoum to Darfur.

The fall of El-Fasher gave the RSF control of all five state capitals in the vast western region, in addition to parts of the south.

The army controls most of Sudan's north, east and centre.

El-Fasher's takeover was accompanied by reports of mass killings, sexual violence and looting, drawing international condemnation.

On Thursday, the RSF said it had agreed to a truce proposal put forward by the United States, Saudi Arabia, the United Arab Emirates and Egypt.

But the United Nations warned the following day of "clear preparations for intensified hostilities" in Sudan, "with everything that implies for its long-suffering people".

The conflict, which erupted in April 2023, has killed tens of thousands of people, displaced nearly 12 million and triggered a hunger crisis.

Both sides have been accused of committing atrocities over the course of the war.