The U.N. human rights chief says Sudanese authorities are restricting press freedoms and making arbitrary arrests, as a referendum approaches on the independence of south Sudan.
Navi Pillay said it is important the referendum is free and fair, calling it a critical moment in Sudan's history.
She urged the governments of Sudan and south Sudan to quickly halt efforts to intimidate voters or taint the result of the referendum, which begins on Sunday.
Nearly 4 million southern Sudanese are registered to vote in the referendum, which will allow voters to secede or remain united with the north. The vote is expected to split Africa's largest country in two.
The referendum is the centerpiece of the 2005 peace deal that ended Sudan's north-south civil war.
Some information for this report was provided by AFP and Reuters.