Sudan said it will not accept a second filling of the reservoir behind the Nile dam being built by Ethiopia until Addis Ababa enters a legally binding agreement on operating it.
Sudanese Irrigation and Water Resources Minister Yasser Abbas said a second filling without an agreement would pose a threat to Sudan’s security.
On Sudanese state TV on Saturday night, Mr Abbas and acting foreign minister Omar Qamareldeen ruled out military action.
Ethiopia's dam on the Blue Nile, which originates in its highlands, was built near the border with Sudan.
The Blue Nile meets the White Nile north of Khartoum, Sudan’s capital, and accounts for 85 per cent of the River Nile’s waters as it flows north through Egypt to the Mediterranean.
Egypt is deeply alarmed that the dam, officially known as the Grand Ethiopian Renaissance Dam, could cut deeply into its crucial share of the Nile waters.
Sudan wants Ethiopia to agree on close co-operation on running the nearly completed hydroelectric dam to avoid flooding or damage to its own power-generating dams on the Blue Nile.
A decade of negotiations between the three nations has yet to produce an agreement on the dam’s operation, a mechanism for resolving future disputes or dealing with persistent drought.
Sudan last month pulled out of the negotiations after Egypt and Ethiopia rejected its proposal that African water and river experts be given a more proactive role in the negotiations.
Mr Abbas said Ethiopia was planning to store 13.5 billion cubic metres during the months of July and August next year, the peak of the annual flood season.
A first filling that took place this year was carried out without Addis Ababa giving Khartoum and Cairo notice.
It involved five billion cubic metres but temporarily affected the volume of water flowing into eastern Sudan from Ethiopia.
“We will not accept from Ethiopia that it goes ahead and starts a second filling in the Renaissance dam without first reaching a binding agreement, and consequently poses a threat to the security of Sudan,” Mr Abbas said.
Mr Qamareldeen said: “The use of force is rejected by Sudan. We will take the option of arbitration if we reach the end of the line without an agreement.”
Egyptian President Abdel Fattah El Sisi also said the dispute would be resolved through negotiations, not force.
But Mr El Sisi never categorically ruled out the use of force, describing the dispute as existential to Egypt, which depends on the Nile for 90 per cent of its water needs.
“Sudan’s withdrawal from the negotiations was designed to highlight a specific position,” Mr Qamareldeen said, suggesting Khartoum could soon return to the next round of talks.
He said Sudanese Prime Minister Abdalla Hamdok was in constant contact with the leaders of Egypt and Ethiopia to narrow their differences.
No date has been set for the next round of talks.