Sudan boycotted talks on Saturday between Nile Valley countries over Ethiopia’s controversial mega-dam, calling on the African Union to play a greater role in pushing forward the negotiations that have stalled for years.

It was the first time that Sudan refused to attend talks with Ethiopia and its northern neighbor Egypt, which has expressed for years its fears that the Ethiopian Grand Renaissance dam on the Blue Nile will dramatically threaten water supplies downstream. 

Sudanese Irrigation Minister Yasser Abbas said in a statement that the current approach to reaching a tripartite agreement on the filling and operation of Ethiopia’s dam had not yielded results, and the AU should do more to “facilitate the negotiation and bridge the gab between the three parties.”

Sudan’s boycott, however, could derail the complicated talks, which the AU has already taken the lead role in supporting.On Thursday, the foreign and irrigation ministers of the three Nile Valley countries met online, two weeks after they failed to agree on a new framework for negotiations.

There were no immediate comments from South Africa, which heads the African Union, Egypt or Ethiopia to Saturday’s move by Sudan. It was not clear when they would restart negotiations.

Ethiopia says the $4.6 billion dam will be an engine of development that will pull millions of people out of poverty. Sudan, in the middle, worries about the effects on its own dams, though it stands to benefit from access to cheap electricity.

Africa’s largest hydroelectric dam has caused severe tensions with Egypt, which has called it an existential threat and worries that it will reduce the country’s share of Nile waters.

Key questions remain about how much water Ethiopia will release downstream if a multi-year drought occurs and how the three countries will resolve any future disputes. Ethiopia has rejected binding arbitration at the final stage of the project.

As well as tension with its Nile Valley neighbors, Ethiopia was plunged earlier this month into a deadly internal conflict when its federal government launched a military attack on the northern Tigray region’s administration.

The conflict threatens to pull in Ethiopia’s neighbors, which include Sudan, Somalia and Eritrea, whose capital came under rocket attack from the Tigray forces over the weekend. The fighting has sent over 35,500 Ethiopian refugees into Sudan.

Ethiopia rejected a U.S.-crafted draft deal over its dam in February and went on with the first stage of filling of the dam’s massive reservoir, leading Washington to suspend millions of dollars in aid to Addis Ababa.