Egypt has denounced Ethiopia’s decision to begin filling the reservoir behind its giant hydropower dam on the Blue Nile for a second year.

The Egyptian irrigation minister, Mohamed Abdel Aty, said he’d received official notice of the filling from Ethiopia and had categorically rejected it.

He said in a statement that the “unilateral” move was “a violation of international laws and norms that regulate projects built on the shared basins of international rivers, including the Nile River”.

The minister has also written to the United Nations Security Council informing it of the latest measure by Ethiopia, the statement adds. The council is due to meet to discuss the matter this Thursday.

Egypt and Sudan had warned Ethiopia that it should wait until they’d all reached a legally binding agreement on the operation of the dam.

Egypt and Sudan, which are downstream, fear the $4bn (£3bn) dam will greatly reduce their access to water. Egypt has been apprehensive that it could disrupt the flow of the river, from which it almost entirely depends on for its fresh water needs.

Ethiopia says the project is vital for its development as it could bring power to 60% of its people.