The UN Security Council has adopted a resolution on the situation in Sudan, promising economic help once peace is established.
The resolution asks the UN, the World Bank and others to devise a long-term development plan, including possible debt relief, for the country.
Long-term plans would require $1.8 billion in aid over three years.
Britain, the former colonial power, has promised $180 million but diplomats doubt any package would reach $1 billion.
The Sudanese government and the Sudan People's Liberation Movement earlier signed an agreement to finalise the end of their 21-year-old civil war by 31 December.
Ambassadors from the Security Council acted as witnesses at the signing, which took place in the Kenyan capital, Nairobi.
The so-called memorandum of understanding pledges to complete a final accord to end the conflict in the oil-producing south of Sudan, which is Africa's biggest country.
The development is also seen as encouraging moves towards solving the crisis in Darfur in western Sudan.
As part of the understanding, the south will have the right to vote on secession in six years' time.
