Wendy Chamberlin, deputy UN High Commissioner for Refugees (UNHCR), said there was a danger donor countries would not deliver promised funds because the world was focused on helping countries hit by the Asian tsunami crisis.
"We've received $3.6 million out of an initial appeal for $30 million, but we anticipate that the needs will be $60 million by the end of the year," Chamberlin said on Sunday during a visit to Sudan.
But she expressed confidence that donors would come through at a conference for Sudan in Norway, due to be held in April.
The two-decade long war, which ended with a peace deal agreed last month, broadly pitted the Khartoum government against the south. It was complicated by issues of oil, ethnicity and religion.
The civil war claimed more than 2 million lives and forced around 4 million from their homes. Most settled in other parts of Sudan, an estimated 600,000 fled the country.
Many of the displaced are expected to return to their homes.
The conflict ended after a peace
deal forged last month
"We will be focusing on the needs of communities of people returning to villages," she said.
The head of UNHCR's Sudan operations, Jean-Marie Fakhouri, said up to 200,000 refugees had already returned south from neighbouring countries since the beginning of 2004.
The government estimates about 400,000 people, who fled to other parts of Africa's largest country, have also returned to their homes in the south.
Chamberlin, a former US diplomat, said the needs of about 2 million displaced southerners living in Khartoum's slums would be assessed and met in their villages if they chose to return.
When asked if there was a danger funds may get diverted from Sudan to cope with the devastation wreaked by the Asian Tsunami, Chamberlin said: "Yes there is ... the focus has been tsunami," she said.
The massive earthquake and flood left some 300,000 people dead or missing when it hit a number of South Asian countries in December.