"Today marks three years since the war in Sudan began," Guterres told a meeting of international donors in Berlin via a video message.

"It is a tragic milestone in a conflict that has shattered a country of immense promise -- and created the world's largest humanitarian crisis."

Guterres noted that "credible allegations of the gravest international crimes" were continually emerging from the conflict.

"Women and girls have been terrorised and systematic sexual violence has prevailed. Families and communities have been devastated," he said.

"The consequences are not confined to Sudan. They are destabilising the wider region... This nightmare must end."

Guterres called for humanitarian workers to be allowed to carry out their work safely and without obstruction, and for humanitarian operations to be fully funded.

"Partners must step up. But let's be clear: funding alone cannot substitute for peace," he said, calling for "an immediate cessation of hostilities".

"External interference and the flow of arms that fuel this war must finally end."