Ethiopian Prime Minister Abiy Ahmed has hailed the "historic" early filling of the massive dam on the Blue Nile River that has stoked tensions with downstream countries Egypt and Sudan.
Addis Ababa had long said it planned to begin filling the dam's reservoir this month, in the middle of its rainy season, drawing objections from Cairo and Khartoum who wanted to first reach a trilateral agreement on how the dam would be operated.
Ethiopia's announcement on Tuesday that it had hit its first-year target for filling the dam came as the three countries were participating in talks overseen by the African Union (AU) to try to resolve the dispute.
"The completion of the first round of filling is a historic moment that showcases Ethiopians' commitment to the renaissance of our country," Abiy, the 2019 Nobel Peace laureate, said in a statement read on state television on Wednesday.
"The fact that we reached this milestone by our own efforts when no one else believed in our capabilities to accomplish such initiatives makes the moment even more historic.
"We conducted the filling of the dam without causing harm to anyone," said Abiy.
The Grand Ethiopian Renaissance Dam has been a source of tension in the Nile River basin ever since Ethiopia broke ground on it in 2011.
Ethiopia said the colossal dam offers a critical opportunity to pull millions of its nearly 110 million citizens out of poverty and become a major power exporter.
Downstream Egypt, which depends on the Nile to supply its farmers and booming population of 100 million with fresh water, asserts that the dam poses an existential threat. Sudan also views the dam as a threat to its water supplies.
After Tuesday's call with the AU, leaders from the three countries said they had agreed to continue with the negotiations, though it was unclear what concrete progress had been made.
In a statement Wednesday morning, Egypt's foreign ministry stressed "the necessity of reaching a binding legal agreement on the rules for filling and operating the Renaissance Dam" that would "include a legally binding instrument to resolve conflicts".
Ethiopia has resisted a legally binding dispute resolution process. Its officials said the dam would not harm downstream countries.
They have also said this year's filling was a natural and inevitable part of construction.
By filling the reservoir with 4.9 billion cubic metres (173 billion cubic feet) of water, Ethiopia is now in a position to test its first two turbines - an important step on the way towards actually producing energy.