CAIRO: Ethiopia has started the second phase of filling the reservoir of its mega-dam on the upper Blue Nile, Egypt and Sudan said, raising tensions Tuesday ahead of an upcoming UN Security Council meeting on the divisive project.

Both Cairo and Khartoum said they had been notified by Addis Ababa that the second phase of filling had begun at the Grand Ethiopian Renaissance Dam (GERD). Egypt’s irrigation ministry late Monday expressed its “firm rejection of this unilateral measure” and Sudan’s foreign ministry on Tuesday followed suit, labelling the move a “risk and imminent threat”. In Addis Ababa, the offices of Prime Minister Abiy Ahmed and Irrigation Minister Seleshi Bekele did not respond to AFP’s requests for comment. The huge dam, set to be Africa’s largest hydroelectric project when completed, has sparked an almost decade-long diplomatic stand-off between Addis Ababa and downstream nations Egypt and Sudan.