Egypt's Foreign Ministry said on Tuesday that the latest round of talks with Ethiopia and Sudan over the Grand Ethiopian Renaissance Dam in Kinshasa have ended with no progress made.
Delegations from the three countries were meeting in the Democratic Republic of Congo hoping to break a deadlock in negotiations over a project Ethiopia says is key to its economic development and power generation.
Egypt fears the dam will imperil its supplies of Nile water, while Sudan is concerned about the dam's safety and water flows through its own dams and water stations.
Before the meetings began, Egypt had said they represented the last chance to restart negotiations before Ethiopia begins to fill the dam for the second year in a row after seasonal rains begin this summer.
Sudan's Foreign Minister Mariam al-Sadig al-Mahdi told reporters on Tuesday that Ethiopia's insistence on such unilateral moves represents a violation of international law.
Ethiopian Water Minister Seleshi Bekele did not respond to texts and calls seeking comment.
Sudan and Egypt were aligned on a proposal to include the European Union, United States and United Nations in the negotiations, as an addition to current African Union mediators.
Egypt said Ethiopia rejected the proposal during the meeting, as well as other suggestions to re-start negotiations.
"This position reveals once again Ethiopia's lack of political will to negotiate in good faith," Egypt's statement said.
Sudan, which is also locked in a border dispute with Ethiopia, had hosted Egypt for air force training exercises that concluded on Saturday.
Last week, Egypt's President Abdel Fattah al-Sissi said there would be "inconceivable instability in the region" if Egypt's water supply were affected by the dam.
"Without a new approach to negotiations, there becomes space for Ethiopia to impose a fait accompli and put all the peoples of the region in grave danger," said al-Mahdi.