The latest truce was due to end late on Sunday April 30, 2023 but the army declared that it is attacking the city from all sides with airstrikes and powerful artillery in order to wipe out its paramilitary competitors
Millions remain trapped in the capital, where food is running short.
Foreign countries have been evacuating their nationals amid the chaos.
More than 500 people have been reported killed since fighting erupted on April 15 between the regular army and the Rapid Support Forces (RSF). But the number of dead and injured may be much higher.
Army commander Gen Abdel Fattah al-Burhan and RSF chief Gen Mohamed Hamdan Dagalo, better known as Hemedti, are vying for power – and disagree in particular about plans to include the RSF into the army.
Thursday night’s agreement to extend an uneasy ceasefire followed intensive diplomatic efforts by neighbouring countries, the US, UK and UN. But the 72-hour extension has not held.
By Saturday evening, heavy fighting had resumed in Khartoum. The army said it had conducted operations against RSF troops north of the city centre.
Eyewitnesses told Reuters news agency that army drones had targeted RSF position near a major oil refinery.
“We woke up once again to the sound of fighter jets and anti-aircraft weapons blasting all over our neighbourhood,” one resident told AFP news agency on Sunday.
BBC diplomatic correspondent Paul Adams, who is monitoring events from Nairobi in Kenya, says the army will find it difficult to expel the RSF from Khartoum.
For all the army’s superior firepower, the RSF are highly mobile and more suited to urban warfare, our correspondent adds.
On Saturday the UK government has ended its evacuation operation. The Foreign Office said the last flight left Khartoum at 22:00 local time (20:00 GMT), and in total nearly 1,900 people were flown out.
A US-organised convoy has reached Port Sudan to evacuate more US citizens by ship to Jeddah in Saudi Arabia. It said hundreds of Americans had already left, in addition to the diplomats evacuated by air a week ago.
Also on Saturday Sudanese former Prime Minister Abdalla Hamdok warned that the conflict could become worse than those in Syria and Libya. Those wars have led to hundreds of thousands of deaths and caused instability in the wider regions.
Speaking in Nairobi, he said: “I think it will be a nightmare for the world. This is not a war between an army and small rebellion. It is almost like two armies.”
Meanwhile, there are chaotic scenes in Port Sudan where people are desperate to board ships, some of which are heading to Saudi Arabia and Yemen.
