Fierce battles broke out on Tuesday across Omdurman, the western part of Sudan's wider capital, as the army tried cut off supply routes used by its paramilitary rivals to bring reinforcements into the city.
The army launched air strikes and heavy artillery, and there were ground battles in several parts of Omdurman, witnesses said. The RSF said it had shot down a fighter jet, and residents posted footage that appeared to show pilots ejecting from a plane. There was no immediate comment from the army.
Conflict between the army and the paramilitary Rapid Support Forces (RSF) erupted on April 15, bringing daily clashes to the capital, triggering ethnically-motivated killings in the western region of Darfur, and threatening to drag Sudan into a protracted civil war.
The RSF quickly took control of swathes of the capital and has brought in extra fighters from Darfur and Kordofan as the conflict has deepened, transferring them across bridges from Omdurman to Bahri and Khartoum, the other two cities that make up the wider capital across the confluence of the River Nile.
Residents said Tuesday's clashes in Omdurman were the heaviest for weeks, and that as the army tried to gain ground it was also fending off an RSF attack against a police base.
"There's been very heavy bombardment for hours, air strikes, artillery and bullets. It's the first time for us that there have been continuous strikes at this level from every direction," said Manahel Abbas, a 33-year-old resident of Omdurman's Al-Thawra neighbourhood.
The conflict broke out amid disputes over an internationally-backed plan for a transition towards civilian rule, four years after the overthrow of long-ruling autocrat Omar al-Bashir during a popular uprising.
Saudi Arabia and the US brokered several ceasefire deals at talks in Jeddah that were suspended last month after both sides violated the truces.
In a move that could escalate conflict in western Sudan, tribal leaders from South Darfur on Monday declared their allegiance to the RSF. The RSF originated in the Arab militias that helped crush a rebellion in Darfur after 2003, before developing into a national and officially recognised force.
Nearly 2.8 million people have been displaced since the start of the fighting in mid-April, including almost 650,000 who have crossed into neighbouring countries, according to the latest UN figures.