Sudanese leaders have taken the vitally important decision that they will work together to build two viable African states, chairperson of the African Union High Level Implementation Panel on Sudan (AUHIP) said on Monday.

These states would be characterised by a high level of co-operation between northern and southern Sudan in all areas, including economy, security, and relations among the people, former South Africa president Thabo Mbeki said.

Sudanese leaders attending the AU Summit meeting in Addis Ababa were determined to do everything necessary between now and the end of the Comprehensive Peace Agreement (CPA) period on July 9 to implement all outstanding CPA provisions as well as negotiate the necessary post-referendum arrangements.

"We have agreed with their Excellencies, President al-Bashir and First Vice President Kiir, that they will engage each other to resolve the issue of Abyei by the end of March," Mbeki said speaking at the AU Summit.

He said matters relating to citizenship would be finalised in the near future.

This would ensure that nobody was rendered stateless and that "no citizen will suffer any negative socio-economic consequences as a result of the formation of the two states.

Citizens would be free to reside where they were at the moment of the separation of South Sudan, Mbeki said.

"The demarcation of the agreed sections of the common border should resume at once and the disputes relating to five areas along the border will be addressed immediately."

Discussions will also take place shortly to develop the details for the functioning of a “soft border”, which would facilitate free movement of people and goods across the common border.

Mbeki said they have every confidence that these eminent leaders and their respective governments, as well as the Sudanese people as a whole, would continue to live up to their responsibilities during the remaining months of the CPA and thereafter.

"We congratulate them and embrace them, and all the people of Sudan, as proud and free Africans, fully capable of determining their destiny and contributing to the renewal of Africa."

Sudan's President Omar al-Bashir, his deputy Kiir, Ethiopian Prime Minister Meles Zenawi and African Union Commission chief Jean Ping attended Monday's meeting, French news agency AFP reported.

President Jacob Zuma and officials from the Intergovernmental Authority on Development (IGAD), a six-member east African regional grouping were also in attendance.

UN chief Ban Ki-moon, who chaired a meeting on Sunday, reminded African leaders of the urgency of issues confronting Sudan, following a landmark referendum in which the south chose to secede.

Ban said all parties "should engage immediately to address all the post-referendum issues," citing border demarcation between the north and south as well as issues of citizenship, security and the sharing of wealth, AFP reported.

South Sudan leader Salva Kiir told the gathering that they were waiting for the world community to acknowledge the outcome of the referendum, which showed overwhelming support for secession from the north.

"We expect this outcome to be confirmed by members of the international community, beginning with those present in this August assembly," Kiir said.

Full preliminary results released on Sunday showed that close to 99 percent of south Sudanese voters chose independence.