Ministers from Egypt, Ethiopia and Sudan said on Friday a final agreement will be signed by the end of February on the giant Blue Nile hydropower dam that sparked a years-long diplomatic crisis between Cairo and Addis Ababa.

The countries have been at odds over the filling and operation of the $4-billion Grand Ethiopian Renaissance Dam (GERD), under construction near Ethiopia's border with Sudan on the Blue Nile, which flows into the Nile river.

The three regional powers convened in Washington for what were supposed to be two days of meetings on Tuesday and Wednesday to complete an agreement after talks earlier this month, but negotiations dragged into Friday and disbanded without a final accord.

In a joint statement with the US and the World Bank after the talks, the nations said they had agreed on a schedule for staged filling of the dam and mitigation mechanisms to adjust its filling and operation during dry periods and drought.

The nations still have to finalize several aspects of the dam, including its safety and provisions for the resolution of disputes, the statement said. But it added that a final agreement on the dam would be signed by all three countries by the end of February.

"Documents to be signed will be further deliberated by legal team supported by technical team. This will continue next week to complete comprehensive document within 30 days," Sileshi Bekele, Ethiopian minister for water, irrigation and energy, said on Twitter.

The US has hosted several rounds of talks in Washington with ministers from the three regional powers and the World Bank after years of trilateral negotiations failed.

US President Donald Trump, in a call with Ethiopian Prime Minister Abiy Ahmed on Friday, expressed optimism that an agreement on the dam was near and would benefit all parties involved, a White House spokesman said.

The dam is the centerpiece in Ethiopia's bid to become Africa's biggest power exporter but has sparked fears in Cairo that Egypt's already scarce supplies of Nile waters, on which its population of more than 100-million people is almost entirely dependent, would be further restricted.

Even without taking the dam into account, largely desert Egypt is short of water. It imports about half its food products and recycles about 25-billion cubic meters of water annually.

Addis Ababa, which announced the project in 2011 as Egypt was beset by political upheaval, denies the dam will undermine Egypt's access to water.