* IOM staff receive menacing letters, calls
* UN monitors urge action, referendum body promises probe
By Andrew Heavens
KHARTOUM, Nov 23 (Reuters) - South Sudanese living in Uganda have received death threats and warnings not to register for a vote on the independence of their region, a development that could undermine the referendum, officials said on Tuesday.
Staff from the International Organisation for Migration (IOM) running the registration have also received menacing calls and letters, disrupting the preparations for January's referendum, said officials.
The Khartoum-based commission organising the plebiscite said it was looking into reports the threats were being made by south Sudanese campaigners trying to limit voting outside the south because they feared the polling there might be rigged.
"There have been death threats by telephone, in letters, banging on doors in the middle of the night," a diplomatic source told Reuters, speaking on condition of anonymity.
The source said the threats were targeting potential voters and staff working for the IOM. The Geneva-based migration organisation declined to comment.
People from the oil-producing south are just 47 days away from the referendum on whether they should secede or stay part of Sudan -- a vote promised in the 2005 peace deal that ended decades of north-south civil war.
Emotions are running high ahead of the vote, due on Jan. 9, that could split Africa's largest country in two. Most south Sudanese are expected to choose independence, but remain deeply suspicious of the former foes in the north.
Leaders from the south's dominant Sudan People's Liberation Movement (SPLM) have accused northerners of plotting to disrupt and rig the poll to keep control of the south's oil.
Senior members of the north's ruling National Congress Party (NCP), which is campaigning for unity, have accused the south of preventing southerners from registering in the north and threatened not to recognise the vote.
Only southerners can vote but registration centres have been set up for an estimated 500,000 eligible voters living in the north and another half million southern people based in Uganda, the United States and six other countries.
"We have heard these allegations that reckless individuals are trying to scare people from voting in Uganda ... The reports are definitely that it is southern Sudanese. They think maybe the process is going to be rigged so they are going out of their way to scare people from registering," said referendum commission member Sabit Alley.
Alley said commission staff were visiting Uganda to check the reports and the progress of the registration. It was too early to say how the Ugandan operation was going, but reports of the threats may have cut registration in rural areas, he added.
U.N. referendum monitors on Monday said they had received "disturbing reports of intimidation and threats" against IOM staff and potential voters.
"We urge the parties (north and south) to help ensure that everyone who wants to register can do so without fear," said former Tanzanian president Benjamin Mkapa heading the panel.
Senior SPLM official Anne Itto on Tuesday told journalists her party had not been involved in any intimidation of voters, without referring specifically to Uganda. (Additional reporting by Jeremy Clarke in Juba; Editing by Giles Elgood)
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