Egypt and Ethiopia, long at odds over plans for a huge dam on the Nile, have made some progress towards a resolution by delaying the filling of the connecting reservoir, sources said.

The two countries, with Sudan, wrapped up two days of talks in Cairo on Tuesday. It was the second of four rounds of negotiations agreed on at a meeting in Washington last month.

Although minor agreements were reached, the nations have yet to iron out differences on how to offset the effects of droughts.

Egypt’s Irrigation Ministry late on Tuesday said very little about the talks or whether they made progress.

The ministry said only that differences would be further discussed in Khartoum in talks scheduled for December 21 and 22.

But officials said Ethiopia agreed to an Egyptian demand that the reservoir behind the dam be filled over seven years to reduce the effect downstream.

The Sudanese government said that differences over filling the reservoir, which has a capacity of 74 billion cubic metres, had narrowed.

The officials said Ethiopia also agreed to another key Egyptian demand that it released 40 billion cubic metres of water a year if the rainfall on its highlands, where the Blue Nile originates, is plentiful or above average.

The fourth and final meeting is scheduled for Addis Ababa in early January.

The ministers are also due to meet in Washington on Monday to assess progress, and again on January 13. Failure to reach full agreement by mid-January will lead to the invitation of a fourth party to mediate.

A mainly desert nation of about 100 million people, Egypt says that a significant drop in its share of the Nile water would affect the livelihoods of hundreds of thousands of farmers, thus threatening the country’s food security.

It also wants Ethiopia to show flexibility during droughts.

But the officials said that Ethiopia and Egypt remained at odds over the definition of a drought. Ethiopia says droughts must be defined as three consecutive years of below-average rainfall.

In Ethiopia, the hydroelectric dam has become a symbol of national pride and is marketed as essential to the nation’s progress.

Egypt acknowledges the importance of the dam to Ethiopia’s development but insists that co-operation is needed to reduce the effect on its share of water.

The dam is built on the Blue Nile, which accounts for 65 per cent of the water reaching Egypt.

It and the White Nile, which originates in Central Africa, meet near Khartoum to form the Nile River, which flows through northern Sudan and Egypt until it drains into the Mediterranean Sea.