Egypt and Sudan on Monday wrapped up six days of war games held against a backdrop of rising tension with Ethiopia over its giant Nile dam.
Cairo and Khartoum fear this project will reduce their share of the river’s water.
The military exercises, named Guardians of the Nile, were held about a month before Ethiopia is expected to begin a second and much larger filling of its dam, despite demands from the two downstream nations that an agreement first be reached on its operation.
Negotiations between the three countries have stalled. The last round of talks in April failed to make any progress – much like numerous rounds held over the past decade.
In comments at the end of the military exercises held in Sudan, the chiefs of staff of Egypt and Sudan made no direct mention of Ethiopia, but made it clear that the drills were meant to send a message to Addis Ababa that they were ready to intervene militarily against the dam if needed.
Egyptian Chief of Staff Gen Mohammed Farid said the exercises were conducted amid “challenges and threats and the possibility of their escalation”.
Involving naval and air force units, as well as ground troops, commandos and air defences, the exercises were intended to upgrade the joint capabilities of and enhance harmony between the two militaries so they can safeguard "our countries' legitimate rights to security, life and development", Mr Farid said.
His Sudanese counterpart, Gen Mohammed Osman Al Hussein, said the drills were far from being routine or strictly within the parameters provided by co-operation agreements.
“They were aimed at realising harmony and entrenching [military] doctrines so that they can be a deterrent to enemies and deal with both expected and potential threats,” he said.
“They are not meant to target anyone specific, as long as our national security is unharmed.”
With the world's 10th largest army and an array of cutting-edge weapons, Egyptian President Abdel Fattah El Sisi has warned that the region would see "unimaginable instability" if the Grand Ethiopian Renaissance Dam, or Gerd, denies his country its full share of the Nile's water.
No one should presume to be out of the reach of Egypt's military, Mr El Sisi said in March.
A former general who was elected president in 2014, Mr El Sisi has stressed that diplomacy was his country’s preferred method of resolving the dispute over the dam, but made it clear Egypt was not prepared to be bogged down in indefinite negotiations.
Egypt depends on the Nile for more than 90 per cent of its fresh water needs. A significant cut in its share of the Nile water could wipe out hundreds of thousands of jobs in the agriculture sector and disrupt its delicate food balance.
Sudan says it faces the threat of destructive flooding if Ethiopia did not co-ordinate with it on the filling of the dam. Its own power generating dams on the Nile could also be affected.