Ethiopia on Saturday hit back at Egypt's "false" claim that it had triggered floods in Sudan by opening the gates of its Nile mega-dam, a regional bone of contention.

Addis Ababa inaugurated its Grand Renaissance Dam (GERD), Africa's largest hydroelectric project, in early September.

Cairo has meanwhile spent more than a decade vehemently criticising the dam over concerns that the "existential threat" will dry up its primary water supply: the Nile, which supplies 97 percent of the water it uses.

On Friday, the Egyptian water ministry said the dam had released "enormous water quantities" immediately after its inauguration, which had "resulted in the flooding of agricultural lands and the submersion of numerous villages" in neighbouring Sudan.

Flooding has affected multiple Sudanese regions including the capital Khartoum for several weeks, which Sudanese authorities attribute to climate change, exceptional rainfall and the opening of the dam's gates.

In a statement published on Saturday, Ethiopia's water ministry called Egypt's statements "false and defamatory" and an attempt to "mislead the international community".

Flooding in Sudan is due to the White Nile tributary's rising water levels and has "nothing to do with Ethiopia", it said.

Ethiopia claims that the mega-dam, located on the Blue Nile tributary which makes up 85 percent of the Nile's waters, may have curbed "historic destruction of human lives and infrastructure" in Sudan and Egypt after heavy rainfall this year.

Pietro Salini, the CEO of the GERD's main contractor Webuild, has said the mega-dam "releases water to produce energy".

"There's no change in the flow. It's just regulated," he told AFP in September.