Aides said Clinton made the calls to Sudan's vice president Ali Osman Taha and Salva Kiir, who heads the autonomous south under the 2005 Comprehensive Peace Agreement (CPA) that ended a 22-year civil war between north and south.
She urged the representatives of the Arab-dominated central government and the south to fully implement the peace deal and prepare for the referendum provided for under the CPA, her spokesman Philip Crowley told reporters.
As a follow-up, the US special envoy for Sudan, Scott Gration, will on Thursday travel back to Sudan to continue the high-level talks, Crowley said.
Speaking to foreign policy experts, Clinton said the United States is also involving the African Union and South Africa as well as European countries Britain and Norway in the diplomatic push to ensure a smooth referendum.
"It's really all hands on deck", the chief US diplomat said during a question-and-answer session following a speech she gave at the Council on Foreign Relations.
"The situation north/south is a ticking time-bomb of enormous consequence", Clinton said.
"The time frame is very short. Pulling together this referendum is going to be difficult", she said.
"But the real problem is, what happens when the inevitable happens and the referendum is passed and the south declares independence?" added Clinton, the highest-ranking US official so far to say secession is a foregone conclusion.
"So simultaneously, we're trying to begin negotiations to work out some of those intractable problems. What happens to the oil revenues?", she asked.
"I mean, if you're in the north, and all of a sudden you think a line's going to be drawn and you're going to lose 80 percent of the oil revenues, you're not a very enthusiastic participant", she warned.
Clinton said the United States is working with both regional and international partners to "figure out some ways to make it worth their while (in the north) to peacefully accept an independent South."
The south will also have to make "some accommodations" with the north "unless they want more years of warfare," she warned.
Semi-autonomous south Sudan is struggling to recover from the war, Africa's longest civil conflict which left an estimated two million people dead and was fueled by ethnicity, ideology, religion and resources such as oil.
The border was meant to be defined six months after the CPA was signed, but negotiations by the committee established to demarcate it are in "deadlock," the International Crisis Group think tank said.
The Brussels-based ICG said last week that some border areas "remain dangerously militarized" as the oil issue raises the stakes for drawing boundaries.
In New York, Susan Rice, US ambassador to the United Nations, said the September 24 meeting Obama, other heads of state and foreign ministers will attend will send "an important signal to the people of Sudan, in the north and south, and Darfur and beyond" about the international commitment to the CPA.
The United Nations says 300,000 people have died in the western Darfur region since minority rebels revolted against the central government in 2003, and 2.7 million people have fled their homes from the fighting.
The government in Khartoum says 10,000 people have been killed.
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She urged the representatives of the Arab-dominated central government and the south to fully implement the peace deal and prepare for the referendum provided for under the CPA, her spokesman Philip Crowley told reporters.
As a follow-up, the US special envoy for Sudan, Scott Gration, will on Thursday travel back to Sudan to continue the high-level talks, Crowley said.
Speaking to foreign policy experts, Clinton said the United States is also involving the African Union and South Africa as well as European countries Britain and Norway in the diplomatic push to ensure a smooth referendum.
"It's really all hands on deck", the chief US diplomat said during a question-and-answer session following a speech she gave at the Council on Foreign Relations.
"The situation north/south is a ticking time-bomb of enormous consequence", Clinton said.
"The time frame is very short. Pulling together this referendum is going to be difficult", she said.
"But the real problem is, what happens when the inevitable happens and the referendum is passed and the south declares independence?" added Clinton, the highest-ranking US official so far to say secession is a foregone conclusion.
"So simultaneously, we're trying to begin negotiations to work out some of those intractable problems. What happens to the oil revenues?", she asked.
"I mean, if you're in the north, and all of a sudden you think a line's going to be drawn and you're going to lose 80 percent of the oil revenues, you're not a very enthusiastic participant", she warned.
Clinton said the United States is working with both regional and international partners to "figure out some ways to make it worth their while (in the north) to peacefully accept an independent South."
The south will also have to make "some accommodations" with the north "unless they want more years of warfare," she warned.
Semi-autonomous south Sudan is struggling to recover from the war, Africa's longest civil conflict which left an estimated two million people dead and was fueled by ethnicity, ideology, religion and resources such as oil.
The border was meant to be defined six months after the CPA was signed, but negotiations by the committee established to demarcate it are in "deadlock," the International Crisis Group think tank said.
The Brussels-based ICG said last week that some border areas "remain dangerously militarized" as the oil issue raises the stakes for drawing boundaries.
In New York, Susan Rice, US ambassador to the United Nations, said the September 24 meeting Obama, other heads of state and foreign ministers will attend will send "an important signal to the people of Sudan, in the north and south, and Darfur and beyond" about the international commitment to the CPA.
The United Nations says 300,000 people have died in the western Darfur region since minority rebels revolted against the central government in 2003, and 2.7 million people have fled their homes from the fighting.
The government in Khartoum says 10,000 people have been killed.
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