Egypt lobbied last year to delay southern Sudan's secession vote for four to six years because it feared the new state could fail and the division could imperil its share of Nile waters, a leaked diplomatic cable showed.
The cable outlined Cairo's warnings that a southern vote for independence in 2011 could have "fatal implications," including destabilising the Horn of Africa, causing an influx of migrants to Egypt, and hurting Suez Canal revenues.
"The result would be the creation of a 'non-viable' state that could threaten Egypt's access to the Nile waters," the October 2009 cable quoted officials as saying.
The plebiscite was promised by the 2005 Comprehensive Peace Agreement, which ended decades of civil war between the north and oil-producing south. It is due to take place on 9 January 2011, but preparations are falling behind schedule.
Egypt's foreign ministry was not available to comment on the cables, which whistleblower WikiLeaks distributed to media.
The WikiLeaks website was down for hours after the company that had been directing traffic withdrew its services late on Thursday, but some cables were published on Lebanese newspaper Al-Akhbar's website.
Egypt said in November it would not object to delaying the referendum for several months.
The leaked cable, from the US embassy in Cairo, said officials asked the US government to "educate" southern leaders on the dangers of separation and encourage them to advocate for unity.
Egypt suggested amending the peace deal to give the south autonomy for ten years before choosing between federation or independence, or delaying the vote for four to six years to develop south Sudan's "capacity for statehood," the cable added.
It said Cairo supported Khartoum's position that a two-thirds majority should be required to split Sudan and that all southerners, including those in Khartoum and the diaspora, should be allowed to vote.
A separate cable from April 2009 quoted Egypt's Intelligence chief Omar Suleiman as telling Admiral Mike Mullen, chairman of the US military's Joint Chiefs of Staff, that "Egypt does not want a divided Sudan."
Egypt, almost totally dependent on the Nile for its water, is locked in a dispute with a coterie of upstream nations over a colonial-era pact that gives it most of the river's annual flow.
Ethiopia, Uganda, Tanzania, Rwanda and Kenya signed a new pact in May and gave the other Nile Basin countries one year to join before putting it into action. Sudan has backed Egypt.
The leaked October 2009 cable described discussions over Nile water sharing as "tense."