Egypt on Wednesday said units of its Air Force and commandos held war games with Sudanese troops, a day after Cairo gave Ethiopia a stern warning over its Nile dam project.
The Egyptian military said the war games, Nile Eagles-2, were held in northern Sudan and had finished.
“The exercise aimed at achieving the maximum use of participating assets in planning and executing air operations and testing the readiness of the forces in carrying out joint operations against targets,” the military said.
Egypt and Sudan last month signed a military co-operation agreement, with Cairo pledging to rush to Khartoum's aid if needed.
The two countries held a series of joint war games over recent months.
Egyptian President Abdel Fattah El Sisi on Tuesday said that denying his country “a drop of water” would cause “unimaginable instability" in the region.
That was his sternest threat yet to Addis Ababa over the Grand Ethiopian Renaissance Dam.
Egypt fears the dam will deeply cut its share of the Nile’s water. With a population of about 100 million, Egypt depends on the Nile for more than 90 per cent of its freshwater needs.
Egypt and fellow downstream nation Sudan have tried for years to persuade Ethiopia to enter a legally binding agreement on the filling and operation of the dam.
Since late last year Sudan and Ethiopia have been tangled in a border dispute that led to deadly clashes.
Ethiopia maintains that guidelines about the dam, rather than a binding deal, should suffice.
It said it planned to proceed with a second and much larger filling of the dam's reservoir in summer, regardless of whether an agreement was reached.
“We don’t talk much but I need to tell everyone that no one can take a drop of water from Egypt,” Mr El Sisi said in the Suez Canal city of Ismailia.
"If anyone wants to try, let him try. But we are not threatening anyone and our discourse remains very patient and very wise, but no one can take a drop of water from Egypt.
"Doing so will create unimaginable instability in the region and no one should assume that he is beyond the reach of our capabilities.
“I say it again, Egypt’s water cannot be touched. Touching it is a red line and our reaction if it’s touched will impact on the entire region.”