The UN's top aid official has warned that the "will to end the fight still was not there" after speaking to Sudan's rival military leaders.

Martin Griffiths told the BBC that Sudan's descent into violence was now at a dangerous tipping point.

He called for security guarantees from the warring sides to allow humanitarian aid into the country.

The UN warns that the fighting could force hundreds of thousands of Sudanese to flee their homes.

In a BBC interview hours after his visit to Port Sudan, Mr Griffiths spoke bluntly of what he called "the rigid existential fact that those at war are keen to keep it going".

During his time in Sudan's largest port, now a major evacuation and humanitarian hub, he had separate telephone conversations with Sudan's rival generals.

Mr Griffiths, the UN Under-Secretary-General for Humanitarian Affairs and Emergency Relief Coordinator, called for their clear public commitments to guarantee urgent deliveries of aid.

"This is about specific protections for the movement of aid workers and goods and supplies - going down roads at certain times, airlifts from being shot down," he emphasised when we sat down in the Saudi port city of Jeddah across the Red Sea from Sudan.

Evacuation ships now arrive daily at the port carrying foreigners and Sudanese, mainly with second passports, fleeing Sudan's sudden descent into rampant violence and wanton looting.

Mr Griffiths described how most of their warehouses storing humanitarian supplies had been looted. Six trucks in an aid convoy heading to the Darfur region were seized en route.

He asked for face-to-face meetings with both General Abdel Fattah al-Burhan, who heads Sudan's armed forces, and his former deputy General Hamdan Dagalo, who commands the rival Rapid Support Forces (RSF).

"I think it's obviously urgent, this should be done in the next day or so," he told us. "We're working on it."

Since 15 April, when the bombs first dropped and bullets flew in all directions, the rival leaders have agreed successive short ceasefires which have repeatedly been violated, especially in the capital Khartoum and the western region of Darfur, which are now war zones.

Mr Griffiths heard the same fine words in his telephone calls where "they were both, separately, very eloquent in their attachment to humanitarian principles and aspirations on the question of where and when we can meet".

Visibly shocked and saddened by what he had seen and heard, he spoke of "tales of traumatic atrocity... that are pretty unparalleled."

"I think a really, really, deeply concerning aspect is the speed with which it is going viral," he added, reaching for words to convey the enormity and intensity of a crisis with profound consequences for the region and the wider world.

"It has got all the makings of a tragedy of global relevance, and global significance. And that is why this is an opportunity for the international community to show that we care about Africa," he underlined with a sweeping perspective of what was at stake in Sudan's crisis.

More than 100,000 Sudanese have already crossed land borders, or the Red Sea, into Sudan's neighbours, and more than 344,000 are said to be displaced across a country where millions have been pinned down by the carnage and criminality.

The UN is warning of a possible exodus of 800,000 with others warning that number could be in the millions.

Mr Griffiths paid tribute to aid workers still on the ground in Sudan, especially local Sudanese civil society and humanitarian agencies, still determined to press on with their urgent humanitarian mission.

"Extraordinary people like those I met today, courageous beyond imagination, operate in areas of great uncertainty," he said, highlighting what he called the humanitarian axiom to "stay and deliver".

The UN's World Food Programme has already seen seven of its staff killed in recent weeks.

Mr Griffiths expressed his shock that even Port Sudan, so far relatively untouched by the fighting, was fragile too.

"Port Sudan is beginning to jump with masses of displaced people, some of them with no prospect of getting out to third countries."

Thousands of Syrians, Yemenis, and Sudanese are now trapped in the port city without the kind of passport, and support, to provide them with a way out.

It's the story of an entire nation struggling to find a way out of this deeply worrying, and rapidly worsening war.

Asked about remarks by the UN Secretary General Antonio Guterres that the UN "failed to stop this war" because it didn't see all the warning signs, Mr Griffiths insisted that "a lot of people didn't see it coming".

"That's yesterday," he declared in the UN's defence. "What we're talking about today, is doing something that is consistent with our values… and meets the needs of the Sudanese people."

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