Crisis mediation is under way to de-escalate the armed violence in Sudan after at least 97 people were killed and 365 injured.
Violence broke out on Saturday in the capital Khartoum and across the country as armed forces and paramilitary group Rapid Support Forces (RSF) clashed.
Three UN World Food Programme (WFP) workers were among those killed in clashes in Darfur.
Two more employees were injured while carrying out duties and a humanitarian aircraft was damaged, “seriously impacting” WFP’s work, a spokesperson said.
The programme has paused while security is reviewed as the spokesperson said there was “no excuse for targeting humanitarian workers”.
Tensions had been escalating between army head and de facto president Abdel Fattah al Burhan and RSF chief Mohamed Hamdan Dagalo, better known as Hemedti.
South Sudan President Salva Kiir and Ethiopian prime minister Abiy Ahmed have had phone calls with both leaders in an attempt to calm the violence.
Egypt and South Sudan have offered to mediate between the army and paramilitary.
Kenyan President William Ruto and Ugandan President Yoweri Museveni have also had phone calls with General al Burhan.
Why has violence erupted in Sudan?
US Secretary of State Antony Blinken has consulted with Saudi Arabian and Emirati counterparts and shared their agreement that it is “essential for all parties to immediately end hostilities”.
The two groups continued their battle for control on Sunday, signalling they were unwilling to end hostilities despite mounting diplomatic pressure.
Heavy fighting involving armoured vehicles, truck-mounted machine guns and war planes raged on Sunday in the capital of Khartoum, its sister city of Omdurman and in flashpoints across the country.
Fighting was reported around military headquarters, Khartoum International Airport and state television headquarters, prompting the channel to cut transmission.
A senior military official said RSF fighters clashed with troops at military headquarters early on Sunday and that a fire broke out at a facility for ground troops.
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Why tensions in Sudan could escalate into ‘all-out civil war’
Former Sudanese prime minister Abdalla Hamdok said: “Peace remains the only feasible choice for the people of Sudan to avoid plunging the country into a civil war.
“We all witnessed the consequences of a civil war in many regions in Africa and in the Arab world. We must avoid that, and we can still avoid such a catastrophic situation. Therefore, I call for an immediate ceasefire and to reach an agreement, which leads to a permanent cessation (of hostilities).”
He also added other countries should not intervene in any negotiations.
Both sides signalled late on Saturday that they were unwilling to negotiate, but on Sunday a statement from the UN said General al Burhan and Hemedti agreed to a proposal for a three-hour pause in fighting (from 2pm to 5pm GMT), to allow the safe passage of humanitarian cases.
Despite the agreement, gunfire could be heard and plumes of smoke seen in the background of live broadcasts.
Hemedti previously told the satellite news network Al Arabiya that he ruled out negotiations and called on the army leader to surrender.
The military called for the RSF to be dismantled, labelling it a “rebellious militia”.