The United Nations on Wednesday urged countries not to forget the civilians caught up in the war in Sudan, appealing for $4.1-billion to meet their humanitarian needs and support those who have fled to neighbouring countries.

A ten-month war in Sudan between its armed forces and the paramilitary Rapid Support Forces (RSF) has devastated the country's infrastructure, prompted warnings of famine and displaced millions of people inside and outside the country.

Half of Sudan's population - around 25-million people - need humanitarian assistance and protection, while more than 1.5-million people have fled to the Central African Republic, Chad, Egypt, Ethiopia and South Sudan, according to the UN.

In the launch of its joint appeal with the UN refugee agency (UNHCR), the United Nations Office for the Coordination of Humanitarian Affairs (OCHA) called for $2.7-billion in funding to provide humanitarian aid for 14.7-million people.

"Sudan keeps getting forgotten by the international community," UN aid chief Martin Griffiths told diplomats at the United Nations in Geneva.

"There is a certain kind of obscenity about the humanitarian world, which is the competition of suffering, a competition between places: 'I have more suffering than you, so I need to get more attention, so I need to get more money.'"

The UN refugee agency asked for $1.4-billion to support nearly 2.7-million people in five countries neighbouring Sudan as part of the appeal.

Griffiths told reporters the warring sides had been invited to Geneva to discuss how civilians can access aid. He said the parties had agreed in principle, but the details of any meeting still needed to be worked out.

OCHA's appeal last year to provide aid to civilians in Sudan was less than half funded. Griffiths said the international community needed to act with a heightened sense of urgency.

"We must not forget Sudan," he said. "That's the simple message that I have to say today."