A court in Khartoum last week ordered journalist Amal Habani to pay a $600 fine or spend one month in jail for reporting on a rape case allegedly involving a member of the state security forces.
She chose the jail sentence and becomes the second person charged recently with defamation for covering suspected rape cases in the country.
Margot Wallstrom, U.N. special envoy on sexual violence in conflict, said journalists have the right to report and rape is still a crime.
"Rapists, not reporters, must face criminal charges in the Sudan," she said in a statement. "Only by addressing sexual violence openly can we have any chance of breaking what has been called history's greatest silence and, ultimately, rooting it out."
South and its neighbor in South Sudan are faced with mounting security problems following the south's independence in July. Border conflicts and issues over oil revenue continue to haunt a comprehensive peace agreement signed between both sides in 2005.
The peace agreement ended a bloody civil war.
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