Ethiopia has banned all flights over its giant new hydropower dam on the Blue Nile for security reasons, the head of its civil aviation authority said on Monday.

Ethiopia is locked in a dispute with Egypt and Sudan over its $4-billion Grand Ethiopian Renaissance Dam, which Cairo has said could threaten its main supply of water.

"All flights have been banned to secure the dam," the director-general of the Ethiopian Civil Aviation Authority, Wesenyeleh Hunegnaw, told Reuters by phone. He declined to give more details on the reasons.

Last week, air force chief Major General Yilma Merdasa told local media that Ethiopia was fully prepared to defend the dam from any attack.

Ethiopia, Egypt and Sudan failed to strike a deal on the operation of the Grand Ethiopian Renaissance Dam before Ethiopia began filling the reservoir behind the dam in July.

The dam is at the centre of Ethiopia's bid to become Africa's biggest power exporter.

The structure is about 15 km (9 miles) from the Ethiopian border with Sudan on the Blue Nile - a tributary of the Nile river, which gives Egypt’s 100-million people about 90% of their fresh water.