The leaders of Egypt, Eritrea and Sudan – three nations accused by Ethiopia of aiding an anti-government rebellion – plus Somalia are meeting on Sunday to shore up their loose alliance.
The Egyptian presidency said the summit was designed to "co-ordinate and consult on regional issues of interest" to the four countries.
However, sources said the meeting would announce several measures to consolidate the alliance of the four nations, including wider military co-operation.
"There may be some surprises in what the four leaders decide in terms of deeper and wider co-operation," said one of the sources.
"One will be broadening the extent of military cooperation to safeguard the region and protect Red Sea shipping."
The summit in Egypt's coastal city of Alamein brings together Egypt's Abdel Fattah El Sisi, Sudan's army chief and de facto leader Gen Abdel Fattah Al Burhan, Somalia's Hassan Sheikh Mohamud and Isaias Afwerki of Eritrea.
Addis Ababa has accused Eritrea, Sudan and Egypt of supporting an opposition alliance led by the Tigray People's Liberation Front that has been battling troops loyal to Ethiopia's federal government. The three nations have denied the charge.
Last week, Egypt and Ethiopia expelled diplomats in a retaliatory row that saw a senior member of each country's embassy ordered to leave.
The expulsions came one day after Ethiopia ordered the closure of its embassy in Eritrea and declared 10 Eritrean diplomats persona non grata. That prompted Asmara to sever diplomatic ties with its neighbour after overnight blasts heard in Addis Ababa sparked fears that the renewed conflict in northern Ethiopia might be spreading.
Egypt has been locked in a bitter, decade-old dispute with Ethiopia over its share of the Nile's waters. Eritrea has been at odds with Addis Ababa for most of the 30-plus years since its secession from Ethiopia. The Sudanese armed forces accuse Ethiopia of aiding its civil war adversary, the paramilitary Rapid Support Forces.
Sudan, Eritrea and Somalia all neighbour Ethiopia and, together with Egypt, have an uninterrupted Red Sea coastline that stretches from the northern tip of the Gulf of Suez in Egypt to Somalia in the Horn of Africa.
Egypt, the most populous of the four nations with an army considered the largest in the Middle East, has been forging close military relations with Eritrea, Somalia and Sudan. It has an estimated 15,000-strong military contingent in Somalia serving in an African Union peacekeeping force as well as a large mission supporting the Mogadishu government and its military.
Egypt's military also has naval and army sites in Eritrea and is reportedly backing the Sudanese Armed Forces against the RSF.
Its military footprint in Eritrea and Somalia is chiefly designed to isolate and put pressure on Ethiopia to show flexibility in their dispute over a large Nile dam Addis Ababa has built that Cairo insists could reduce its vital share of the river's water.
Labelling it an existential issue, Egypt says any reduction would have a disastrous impact on its economy, wiping out millions of agricultural jobs and disrupting its delicate food balance.
Egypt is also engaged in an intense campaign to prevent efforts by landlocked Ethiopia to secure a permanent foothold on the Red Sea.
