Ethiopia said on Tuesday that "threats" by Egypt and Sudan amid deadlocked negotiations over Addis Ababa’s Grand Ethiopian Renaissance Dam (GERD) were “futile”, rejecting historical agreements on shares of the Nile waters upheld as points of reference by the two downstream countries in the talks.

Ethiopian Foreign Ministry Spokesperson Dina Mufti accused in press statements Egypt and Sudan of not seeking the success of an African Union (AU) mediation of the GERD under the chairmanship of the Democratic Republic of Congo (DRC).

He accused Egypt and Sudan of "prolonging" talks with Addis Ababa in the past period  and “exiting them on nine different occasions."

“We rely on the resumption of talks on the dam through the AU,” he said, adding that negotiations are held only on the filling of the dam.

Muftit said historical agreements used as reference points by Egypt and Sudan during the talks were “unacceptable”.

The historical treaties Mufti is referring to include the 1959 Egypt-Sudan Nile waters agreement, which allows both countries full, rather than partial, use, of Nile waters, and confirms Egypt’s right to 55.5 bcm annually, and Sudan to 18.5 bcm.

The 1959 agreement supplements the 1929 Nile Waters agreement, which saw Egypt and Great Britain, which represented Uganda, Kenya, Tanzania, and Sudan at the time, sign an agreement that gives Cairo the right to veto projects higher up the Nile that affect its water share.

Egypt has repeatedly rejected Ethiopia's attempts to include the renegotiating of the Nile Water agreements in GERD talks.

Mufti’s statements come days after Sudan waved at a legal action if Ethiopia moves forward with the second filling of the dam in July without first signing a legally binding agreement.

Sudanese Irrigation Minister Yasser Abbas said on Friday that if Ethiopia moves forward with the second filling without reaching a deal, Sudanese legal teams will sue the Ethiopian government and the Italian company constructing the dam with the help of an international law firm.

His statements came days after Ethiopian Prime Minister Abiy Ahmed proposed a meeting by the Bureau of the Assembly of the AU to end the ongoing stalemate over the dam, as his country rejected an invitation by Sudan for tripartite talks with Egypt to discuss means to revive the GERD negotiations.

Tensions have mounted in the past weeks after the latest trilateral round of talks in Kinshasa earlier in April failed to produce an agreement to re-launch deadlocked negotiations.

Ethiopia’s rejection of several proposals by Egypt and Sudan on the negotiation mechanism, which includes an international quartet mediation, has led to the collapse of the Kinshasa talks.

The three countries have resorted to diplomacy in the past weeks, briefing regional and international counterparts on their stances and developments on the latest deadlock in negotiations.

They have all sent letters to the UN Security Council (UNSC) to clarify positions and developments on the dam, and exchange accusations over the falter of the talks during the decade-long crisis.

Egypt sent its foreign minister on a six-nation tour in Africa to clarify the country’s stance in the GERD dispute, with Sudan set to send its foreign minister on a similar African tour this week to also brief several African capitals on Khartoum's stance on the crisis.

Addis Ababa plans to move ahead with the second filling of the dam despite the objections of Egypt and Sudan to the move in the absence of a legally binding deal.

The second filling is meant to amass around 18.4 bcm of Blue Nile water in the GERD reservoir, up from the 4.9 bcm secured during the first filling last year.

Egypt’s President Abdel-Fattah El-Sisi has repeatedly called on Ethiopia not to compromise Cairo’s share of Nile water, saying “all options are open,” and stressing that “cooperation is better than fighting.”

El-Sisi said earlier in April that failing to resolve the dam crisis will negatively impact the security and stability of the region.