GENEVA - One of Africa's most protracted refugee situations may be further stalled unless donors help send home 24,000 Mauritanian refugees, many of whom have spent nearly two decades in exile, the United Nations said on Tuesday.

The U.N. High Commissioner for Refugees (UNHCR) said it had received only $500,000 towards its $7 million appeal to finance a voluntary repatriation programme for Mauritanian refugees, who are mainly in Senegal and Mali.

More than 60,000 Mauritanians fled their homeland in 1989 following ethnic purges by the Arab-dominated government of former dictator Maaouya Ould Sid'Ahmed Taya. Over the years, 35,000 have gone home on their own and a democratically-elected government in June invited the rest to come back.

"We fear serious delays in the programme," UNHCR spokeswoman Jennifer Pagonis told a news briefing. She said the intended 17-month repatriation programme would "help resolve one of the most protracted refugee situations in Africa".