The announcement gives the SPLM an even stronger grip over southern politics [Gregg Carlstrom/Al Jazeera]

Juba, Sudan — The southern branch of Sudan's ruling National Congress Party (NCP) has said it will split with the northern party and join the Sudan People's Liberation Movement (SPLM), the ruling party in the south.

Riak Gai, the head of the NCP in Southern Sudan, said on Thursday that the split would take effect immediately.

The decision, coming just two days before South Sudan becomes an independent nation after January's referendum, will affect not just the southern parliament, but state governments as well, Gai said.

"Because my people have chosen independence from the north, we have also decided to delink from the NCP," he said at a press conference in Juba, the soon-to-be southern republic's capital. "This is not an individual decision… but a decision taken by the NCP at all different levels."

Barnaba Marial Benjamin, the south's minister of information, said the announcement showed a commitment to open democracy. "The SPLM and the NCP can move past their differences," he said.

Gai also said that South Sudan would benefit from political competition, but stressed the importance of "unity” heading into Saturday's secession from the north.

"We in South Sudan, we need unity," he said. "Although we need pluralism too, but I think the right course of action for us is to join hands with our brothers and sisters in the SPLM."

A one-party state?

Despite Gai's ode to pluralism, the decision to join the SPLM further cements the party's control over southern politics.

The Comprehensive Peace Agreement, the 2005 deal that ended Sudan's decades-long civil war, gave the SPLM 70 per cent of the seats in South Sudan's parliament and its state governments. The SPLM further consolidated its grip on power during last year's election, when it won nearly 90 per cent of the seats in the southern parliament.

"Given its beginnings as a rebel movement during the south's long struggle, it is also the most broadly recognised and supported political entity," the International Crisis Group wrote in a report earlier this year. "It so dominates institutions of government that separating the SPLM from the [government of Southern Sudan] is no easy task."

Thursday's announcement means little in South Sudan's legislature, because the NCP only holds one seat.

It is more significant at a state level, party officials say, because it gives the SPLM further control over bureaucracies. The SPLM already holds nine of the 10 state governorships in Southern Sudan.

Southern Sudan will become an independent nation on Saturday, after which hundreds of southern officials serving in the northern government are expected to return home.