Ethiopia’s prime minister and Sudan’s leadership said on Tuesday they would make every effort to reach a deal on a giant hydropower dam on the Blue Nile that has caused a bitter dispute between Addis Ababa and Cairo over water supplies. Ethiopia, Egypt and Sudan failed to strike an agreement on the operation of the Grand Ethiopian Renaissance Dam (GERD) before the reservoir behind the dam began being filled in July. But the three countries have returned to talks under African Union mediation.