New York (CNN) -- An international advocacy group is warning that 1.5 million to 2 million southern Sudanese now living in the northern part of their country could face persecution if the south approves a referendum next year to secede.
Refugees International said in a new report that the issue of post-referendum citizenship was not being adequately addressed by international organizations involved in the country, including the United Nations and the American government.
There is a dangerous possibility, the report said, that the issue will "not rise to the same level of importance as oil revenue and border demarcation."
If the January 2011 referendum passes, as is widely expected, people who are now considered internally displaced could become refugees overnight. Southerners who now live in the north would be "key targets for post-referendum violence," said the report.
"International actors need to think in concrete terms about the possible risks to vulnerable communities," said Joel Charny, vice president for policy at Refugees International and a co-author of the report.
The southern population living in the north is centered in and around Khartoum, Sudan's capital. Though some of the population is relatively affluent, including many university students, the majority is lower-class and works in the underground economy.
This population is already routinely discriminated against, said the organization. This ranges from being denied housing, employment and government services, to being forcibly moved from the city center to surrounding countryside.
At best, southerners living in the north would have to leave the jobs and lives they established in that area. At worst, they could lose their property and be subject to violent attacks, according to the advocacy group.
Refugees International called on the United Nations to make citizenship issues among their top priorities. It also made an appeal to international donors to help fund a survey of southerners living in the north to better asses their post-referendum intentions.