The latest round of talks between north and south Sudan over the future of the oil-producing Abyei region has failed to reach an agreement.

The issue stands as a key hurdle ahead of referendums in the country, and according to the north's National Congress party (NCP) and the south's ruling Sudan People's Liberation Movement (SPLM), "serious efforts and many productive discussions, [the delegations] did not succeed in reaching agreement on the eligibility criteria for voters in the Abyei Area referendum".

The NCP and SPLM also said in a joint statement on Tuesday that both parties "will meet again in Ethiopia toward the end of October to continue their discussions. The parties continue to commit themselves to their mutual goal of avoiding a return to conflict".

Local residents in Abyei will vote on whether the region should join north or south Sudan in a plebiscite scheduled for early next year, which was promised as part of the 2005 peace deal that ended decades of north-south civil war.

The vote is set to be held alongside south Sudan's referendum on independence from the north.