With its rich grazing pastures, oil fields and history of tribal animosities, Sudan's Abyei could tip the country into civil war after northern troops seized control of most of the disputed district.
The north's troops took control Sunday of Abyei's main town and the Bahr Al-Arab area, expelling the south's Sudan People's Liberation Army (SPLA) and raising concern about the implications for peace between the two sides in the run-up to international recognition of southern independence in July.
Key facts on Abyei
The 2005 Comprehensive Peace Agreement ended 22 years of devastating civil war between north and south which requires both sides to keep their troops out of Abyei until a vote to determine its future.
Fighting in Abyei has pitted former civil war enemies against each other since January when it was due to vote on its future alongside a referendum on the south's secession that delivered a landslide for splitting Africa's largest nation in two.
But Abyei's plebiscite was postponed indefinitely as the north and south disagreed on who should be eligible to vote in an area where conflicted loyalties and land disputes keep tensions high.
The former southern rebels, the Sudan People's Liberation Movement (SPLM) and their tribal allies, the Dinka Ngok, remain at loggerheads with the Misseriya pastoralists and the north's ruling National Congress Party (NCP) over who should be allowed to vote.
The flashpoint border region, with some of Sudan's biggest oil-fields nearby, has long been a source of north-south tension.
After the peace deal was signed, Khartoum and Juba agreed to set up a commission to demarcate the borders of Abyei, which is the heartland of the Dinka Ngok, but its findings were contested.
In 2009, the two sides referred the issue to the Permanent Court of Arbitration based in The Hague, which reduced the region to an area of about 10,000 square kilometres (3,860 square miles) and left out the Heglig oil fields.
The ruling was welcomed by the SPLM, the Dinka Ngok and the NCP, which had secured its coveted oil fields. But it was rejected by the Misseriya, which fought for the north in the 22-year civil war.
The NCP subsequently reneged on its commitment and agreed to support the claims of their former civil war partners.
A tribe of Arab nomads, the Misseriya have long migrated to Abyei with their cattle during the dry season to take advantage of its grazing land and water from the Bahr al-Arab river — or Kiir river to the southerners.
Under the referendum law, the Dinka Ngok are eligible to vote, but not the Misseriya, who fear they may lose access to the waters if Abyei joins the south.
With both sides heavily armed, renewed tensions could flare up in the area as they did in May 2008, when the worst fighting to rock the 2005 peace accord displaced 60,000 people and flattened Abyei town.
Negotiations between the SPLM, the NCP, the Dinka Ngok and the Misseriya aimed at breaking the Abyei deadlock have yet to bear fruit.
Analysts issue warning
Analysts warn the two sides are becoming radicalised and that the impasse has worrying implications for Sudan's other unresolved border disputes.
"The implications it has for the wider north-south boundary and the international border this might become are dire. This is why Abyei still matters," Douglas Johnson, an expert on southern Sudan, said in a study.
Sudan's north-south border runs to more than 2,000 kilometres (1,250 miles), but its demarcation is one of the key outstanding issues between the two sides, with some 20 per cent yet to be agreed on.
The Misseriya, some of whom blocked a road used by southerners returning home in December and briefly kidnapped a Chinese oil worker, usually begin their seasonal migration to Abyei in early January.