The electoral body tasked with organising next January's referendum on south Sudan's independence has said that the vote might be delayed.
Mohamed Kahlil, who heads the Southern Sudan Referendum Commission, told Al Jazeera on Sunday that meeting the January deadline appeared "difficult".
"Even if we had the initial voters registration records available and published today, conducting the referendum on the current deadline will still be difficult," Kahlil said.
"For now, the referendum commission wants to focus on its work and leave the deadline issue to the political decision makers."
Several unresolved disputes are threatening the planned vote.
One of them is the row between the ruling National Congress Party (NCP) and the south's Sudan People's Liberation Movement (SPLM) over whether the contested 2,100km border must be demarcated before the referendum.
Voters not registered
Voter registration also still needs to take place and it is not yet clear if southerners living in the north can cast ballots.
On Friday, Southern Sudan cabinet refused to postpone the referendum and its chief negotiator with the NCP government on the referendum said postponement of the vote was not an option.
He said his party would pursue "other options" instead of having the referendum delayed.
Sudan is divided between the north, which is led by Omar al-Bashir's NCP, and the south which is led by the SPLM, but is still seeking full independence.
A 2005 Comprehensive Peace Agreement which ended the SPLM's decades-long guerrilla campaign against the Khartoum government allowed the south to have its own government and to hold a referendum for independence.
Pagan Amum, the secretary-general of the SPLM, said in an interview that his party would continue to engage the north to overcome any obstacles.
"We want to carry out the referendum on date. We do not accept any delay ... not for one hour," he told Al Jazeera.
"If there is any attempt to postpone the referendum, the people of Southern Sudan will take their own decision through their representatives based on the comprehensive peace treaty."
In 2007, the southern ministers walked out of the government in protest against what they considered to be Khartoum's foot-dragging in implementing key points of the 2005 agreement.
It took two months to resolve the differences and the SPLM accused the northern government of not sharing the country's oil wealth, not pulling troops out of southern Sudan, and remilitarising contested border zones where the main oil reserves are located.
Amum said his party will "choose the mechanism through which people will express their vote" because "we want to ensure that there is peace, no war".
Tensions have been rising over the stalled preparations for the vote.
Al Jazeera's Mohamed Adow, reporting from Sudan, said: "There are so many issues to be resolved before the vote takes place. But delaying this referendum is a very big risk, because of the high expectation of the people of southern Sudan.
"If the commission makes official postponement request at the end, it would be up to the ruling National Congress Party and SPLM. [But] these two parties are highly unlikely to approve a postponement."