JUBA, Sudan (AP) — A top leader in Southern Sudan warned Friday that the Sudanese government risks the collapse of a peace accord that ended a war that killed more than 2 million people if it stalls an independence referendum for the south scheduled for January.

Southern Sudan is eagerly awaiting the vote, which could turn the arid region into the world's newest nation and split Africa's largest country in two. A 2005 peace agreement that ended four decades of on-and-off war between Sudan's north and south called for the referendum for southern Sudanese. But negotiations have barely begun and tensions are rising.

It took months of talks between the north and south before the commission charged with organizing the vote was in place. Now it's deadlocked over the appointment of the secretary general of the commission.

Pagan Amum, a top negotiator and official for the southern Sudan Peoples' Liberation Movement — a former rebel group — said the south will reject any attempt to delay the Jan. 9 referendum. He stressed the importance of negotiations to ensure that Sudan "does not return to conflict." He told a news conference that he wants amicable relations between the two regions.

Posters and billboards that blanket Juba — the former war-devastated garrison town turned upstart capital city — champion secession.

"It's very clear for all southern Sudanese — we want separation," said Mabior Achiek, a soldier who was wearing a "Referendum Now" T-shirt. "What I know is that we had war ... and we may have to fight again to get our referendum because the NCP doesn't want it to happen."

He was referring to the ruling National Congress Party, based in Sudan's capital Khartoum.

A northern official on the referendum commission has warned that there is not enough time to prepare for the referendum. But the chairman of the commission, Mohammed Ibrahim Khalil, a northerner, said this week that the commission only deals with legal and constitutional issues and is not empowered to delay the vote.

Marial Benjamin, the south's minister of information, accused the NCP of "trying to make obstacles so everyone will think it should be postponed. But the government of Southern Sudan thinks it should be on time."

Many in the hot , dusty town of Juba say the northern government ignored the south for years — one of the reasons southerners widely back secession. Trash fills the streets, most of which are unpaved. Some aid workers reside in shipping containers while residents on the outskirts live in mud huts.

"If the NCP had developed the south, then maybe we could have gone for unity," said university student Andrew Juach.

The United Nations Mission in Sudan, a $1 billion-a-year peacekeeping operation, helped monitor and implement the complex 2005 accord and aided Sudan's April presidential, parliamentary and local elections. David Gressly, the top U.N. official in the south, says the world body is prepared to play a "very expansive" role in the independence referendum.

"We are not yet to the point where it can't occur on time," Gressly said. "But some practical decisions will need to be made quickly. If we did the elections, we can do this one."

Voter registration still needs to take place and it's not yet clear if southerners living in the north can cast ballots.

A central dispute between the northern NCP and southern SPLM is whether the contested, 1,300-mile (2,100 kilometer) border must be demarcated before the referendum.

Amum insists the secession vote is not conditional on border demarcation, but Sudanese Foreign Minister and NCP member Ali Karti says the border must be set first to establish where people live and which nation will control natural resources like oil.

The peace agreement also promises a separate referendum for the people of Abyei — a long-contested, oil-rich area that straddles part of the expected north-south border and was the site of a clash between the northern and southern armies in 2008. Abyei residents will vote to decide whether they join the north or south but an Abyei commission hasn't been formed yet.

A top official in Abyei recently accused the Khartoum government of resettling tens of thousands of Arab nomads in the area to alter the population and tip the vote in the north's favor.