Gunfire could be heard in several parts of Khartoum and eyewitnesses said gunfire was also heard in adjoining cities.
A Reuters journalist saw cannon and armoured vehicles deployed in streets, and heard the sound of heavy weapons fire in the vicinity of the headquarters of both the army and RSF.
Earlier, the RSF said the army had surrounded one of its bases and opened fire with heavy weapons.
The violence followed days of tension between the army and the RSF, a powerful paramilitary group headed by General Mohamed Hamdan Dagalo, better known as Hemedti. This had sparked concern about a confrontation that would undermine long-running efforts to return Sudan to civilian rule after power struggles and military coups.
The rift between the forces came to the surface on Thursday, when the army said that recent movements, particularly in the northern town of Merowe, by the RSF had taken place without coordination and were illegal.
On Saturday there was a heavy exchange of gunfire in Merowe, eyewitnesses told Reuters.
A statement by the RSF on Saturday called the army’s actions a “brute assault” and called for it to be condemned. It said that the RSF had been in contact with local and international mediators to inform them.
The RSF, which together with the army overthrew long-ruling autocrat Omar al-Bashir in 2019, began redeploying units in Khartoum and elsewhere amid talks last month on its integration into the military under a transition plan that would lead to new elections.
A confrontation between his forces and the army could spell prolonged strife across a vast country already dealing with economic breakdown and flare-ups of tribal violence.