The Sudanese government said the unilateral filling of the GERD and the recent operation of one of its turbines for power generation are “incompatible with the spirit of cooperation,” Sudan’s official news agency SUNA cited Omar Kamel, spokesman for Sudan’s GERD negotiating team, as saying on Monday.

Kamel added that Ethiopia’s unilateral measures also violate the Declaration of Principles (DoP) signed between Addis Ababa, Cairo and Khartoum in 2015.

The DoP, signed in March 2015 by the three countries in Khartoum to settle the GERD crisis, granted Ethiopia the consent of the two downstream countries to construct the dam in return for a pledge from Ethiopia that the project would cause no harm to Sudan and Egypt.

The 10-principle DoP obliges the three countries to take all the necessary procedures to avoid causing significant damage them while utilising the Blue Nile.

On Sunday, Ethiopian Prime Minister Abiy Ahmed congratulated Ethiopians as the GERD's first turbine began generating power, a step that Egypt has also described in an official statement as a violation of the 2015 DoP.

“This is good news for our continent and the downstream countries with whom we aspire to work,” Ahmed said.

Kamel cited Ahmed’s remarks, saying that “Sudan believes that it is necessary and important for Ethiopia to take real steps that correspond to these remarks on the ground.”

Egypt and Sudan have frequently highlighted the necessity that a legally-binding agreement is reached with Ethiopia on the filling and operation of the dam, a demand that Ethiopia has brushed away several times.

Egypt, which relies mainly on the Nile for its water needs, fears that the unilateral and quick filling and operation of the GERD would have a negative impact on the country's water supply. Meanwhile, Sudan is concerned about regulating water flows to safeguard its own dams.

However, Ethiopia implemented the first two phases of filling the mega dam on the Blue Nile over the past two years without the two countries’ consent.

In January, the upper stream country voiced plans to remove 17,000 hectares (40,000 acres) of forest around the GERD ahead of the third filling of the dam’s reservoir during the next rainy season in July.

“Sudan reiterates its fixed stance on the GERD file regarding the necessity to reach a legal agreement on the filling and operation of the GERD,” Kamel said, affirming that its stance is based on international law and the 2015 DoP.

The Sudanese government also welcomes Senegal’s taking over of the presidency of the African Union this year and calls for enhancing the role of the AU, the sponsor of the GERD negotiations, Kamel said.

“This should come in a way that enables the parties [involved in the GERD dispute] to reach an agreement within a specific timeframe and ensures the change of the current negotiations methodology,” the Sudanese statement added.

A presidential statement by the United Nations Security Council (UNSC) in September called for the three countries to reengage in AU-sponsored talks to reach a deal that would end their decade-long stalemate over the GERD.

The three countries have expressed willingness to resume their talks under the auspices over the AU, which collapsed in recent years and stopped last April after the latest round of talks in Kinshasa failed to achieve a consensus.

The two downstream countries have blamed the talks’ failure on Ethiopia’s “intransigence.”

“Sudan affirms that its participation in all rounds of negotiations stems from its conviction that an agreement can be reached that takes into account the interests of the three parties,” Kamel said.

The now-operating first turbine generates 375 megawatts, while the second turbine is also in preparation, the Ethiopian News Agency reported, adding that when the construction of the dam is complete, it will generate 5,250 megawatts of electricity.

The Ethiopian PM said on Sunday that "from now on, there will be nothing that will stop Ethiopia," according to AP.