Sudan's army has withdrawn from negotiations with the Rapid Support Forces, saying the rival paramilitary group has failed to honour conditions for a truce mediated by Saudi Arabia and the US, it said on Wednesday.
The decision could exacerbate fighting in the war that began on April 15.
It also underlines the army's apparent intention to press on in a conflict that has yet to produce a winner or even one side with an edge over the other.
"It is a worrying sign that the talks are nowhere near producing a permanent ceasefire," Michael Hanna, the New York-based director of the US programme in the International Crisis Group, told The National of the army's decision.
"The bigger concern now is that the Sudanese army may be gearing up for an escalation to try to produce a military outcome,. Preventing a surge in the fighting would test the capacity and leverage of external parties, he added.
Meanwhile, the closure of Sudanese airspace will be extended until June 15, Khartoum international airport said on its Facebook page on Wednesday.
"Aid and evacuation flights will be excepted from this decision after securing permissions from relevant authorities" the statement said.
Residents on Wednesday reported renewed fighting in parts of Khartoum, in breach of the truce.
"The general command of the armed forces has decided to suspend [participation in] the current talks in Jeddah due to the rebel militia's lack of commitment in implementing any of the terms of the agreement and its continuous violation of the ceasefire," the army said.
A diplomatic source, who is briefed regularly on the progress of the talks in Jeddah, told The National that the army had specifically cited the continuing occupation by the RSF of health facilities in Khartoum as well as private homes and government buildings.
The army also cited what it called the RSF's obstruction to the delivery of relief supplies to millions trapped in Khartoum with little food and water, and frequent power cuts.
The war has forced nearly 1.4 million people to flee their homes, including more than 350,000 who have crossed into neighbouring countries.
The decision to pull out of the Jeddah talks came after the two warring parties agreed to a five-day truce that took effect on Monday but was broken by both.
Negotiations began early this month and had produced a declaration of commitments to protecting civilians and forming humanitarian corridors under two short-term ceasefire deals that were repeatedly breached.
The negotiations from which the army pulled out were focused on better implementation of the existing truce and extending it for a longer period to allow the delivery of aid to civilians.
The previous truce expired on Monday but was renewed hours before it was due to end.
Beside Wednesday's clashes, residents reported heavy fighting throughout Tuesday evening in Khartoum and its adjoining twin cities of Omdurman and Bahri, as army chief Gen Abdel Fattah Al Burhan vowed to fight the RSF to the end.
The truce was brokered and is being monitored remotely. Both Washington and Riyadh say it has been broken by both sides but has still allowed for the delivery of aid to an estimated two million people.
Speaking to soldiers in Khartoum on Tuesday, Gen Al Burhan warned that the military has yet to use what he called its “maximum firepower” in the six weeks of war.
He said the army does not want to destroy the country, but maximum power would be used "if the enemy does not succumb.
"We will continue to fight until the last soldier standing is killed,” he added.
The senior diplomatic source said the army's chief negotiator in Jeddah, career diplomat Omar Siddiq, handed US and Saudi mediators an exhaustive report backed up with video footage citing RSF breaches of successive ceasefires.
The report identified 22 health centres occupied by the RSF in Khartoum, which have been put out of service; and cited the occupation by the paramilitary fighters of a major oil refinery north of Khartoum.
The report was also said to have included footage of RSF fighters occupying government buildings and homes, effectively using civilians as human shields.
RSF fighters have since the early days of the war deployed on the streets in residential areas following the destruction of their bases by the army's air force. They have, according to witnesses, helped themselves to shuttered grocery stores, abandoned homes and