People from the south are widely expected to choose independence in the vote due to take place from Jan. 9, but Egypt's President Hosni Mubarak and Libya's Muammar Qaddafi have both called in the past for the nation to remain united.
The leaders, whose countries share long, porous desert borders with Sudan, were due to meet Sudanese President Omar Bashir and the leader of the semi-autonomous south, Salva Kiir.
Leaders of the north's ruling National Congress Party (NCP) and the main southern party, the Sudan People's Liberation Movement (SPLM), have talked for months about the location of their common border, how to split oil income and other issues.
But there has been little public sign of progress. Both sides have accused the other of building up troops, and analysts say disputes over preparations for the vote could reignite conflict, threatening the entire region's stability.
"They know the stability of Sudan will reflect positively on Libya and Egypt," Sudanese Information Ministry official Rabie Abdelati told Reuters.
"They are coming to smooth out the differences between the NCP and the SPLM."
The plebiscite was promised in a 2005 peace deal to end decades of civil war between the mostly Muslim north and the oil-producing south, where most people follow traditional beliefs and Christianity.
