Foreign and water ministers from the two countries and Sudan have been meeting in Washington for the last two days to hammer out a final deal on how the dam will operate.

A draft agreement on 15 January, brokered by the US Treasury Department and the World Bank, noted that the mega dam on the River Nile should be filled in stages during the rainy season.

But it did not specify the time frame for implementation, with finer details expected be worked out in the final agreement.

The issue of how the dam is to operate has been contentious for years.

Ethiopia considers the project as critical to its energy needs and wants the dam to be filled and be operational as soon as possible.

But Egypt, which relies on the Nile for 90% of its water needs, has serious concerns that its supply would be compromised should the dam be filled too fast.

Ethiopia, which began construction of the $4bn (£3bn) dam in 2011 on the Blue Nile, a tributary that contributes 85% of the Nile waters, has always said it wants the dam to be filled within six years.

Egypt has maintained that a longer period - of between 10 and 21 years - would be better so that the water flow is not drastically reduced.

Ethiopia and Egypt have not yet agreed over the dam.