UN human rights chief Navi Pillay on Thursday urged authorities in Sudan to ensure that intimidation and abuse do not mar a historic referendum on independence for the south that begins this weekend.
In an appeal addressed to authorities in both Khartoum and the south, the UN High Commissioner for Human Rights said there was "cause for cautious optimism" following recent statements by Sudanese leaders.
"Nevertheless, the run-up to the referendum has been marked by some worrying trends, including restrictions in press freedom and a number of arbitrary arrests and detention," she said.
Pillay also expressed concern about reports of "provocative statements" by state officials about the future of Southern Sudanese living in the North.
She called on authorities to ensure that the vote "is not marred by any abuses of voters’ rights before, during or after the referendum."
"This is a critical moment in Sudan’s history," Pillay said.
"It is essential that the vote is free and fair, and that the national government and the government of south Sudan take swift and effective measures to halt any attempts to intimidate any groups or individuals, or to subvert the result," she said.
Almost four million southern Sudanese, who live in the south, north as well as abroad, are registered to participate in the January 9-15 referendum, which will allow them to decide on whether to secede or to remain united with the north.
The predominantly Muslim north and largely Christian-influenced south fought a bitter 22-year civil war that left more than two million people dead and forced four million to flee before a peace deal in 2005.
Pillay urged authorities to "guard vigilantly" against intimidation of more than 1.5 million southern Sudanese living in the north, as well as against northerners living in the south.
During a visit to the southern capital Juba on Tuesday, Sudan's President Omar al-Bashir said he would celebrate the results even if the south chooses to secede, and pledged to help build a secure and "brotherly" southern state if it votes for independence.