Somalia will hold an emergency Cabinet meeting on Tuesday, state media said, after the breakaway region of Somaliland struck a controversial deal with Ethiopia giving Addis Ababa access to the Red Sea.
Monday's surprise pact has triggered fury in Mogadishu, which considers it a violation of its sovereignty.
It was announced only days after Somalia's central government had agreed to resume dialogue with the separatist northern region after years of stalemate.
Somaliland has been seeking full statehood since claiming independence from Somalia in 1991, a move fiercely opposed by Mogadishu and not recognised internationally.
The Addis Ababa agreement gives landlocked Ethiopia long-desired access to the Red Sea, a key waterway for global trade.
"This historic agreement ensures Ethiopia's access to the Red Sea for their naval forces, reciprocated by formal recognition of the Republic of Somaliland, marking this as a significant diplomatic milestone for our country," Somaliland's foreign ministry said in a statement.
Somali National Television said on X, formerly Twitter, that there would an emergency cabinet meeting on Tuesday to discuss the agreement.
There has been no immediate reaction from President Hassan Sheikh Mohamud's office, but his predecessor Mohamed Abdullahi Mohamed, better known as Farmajo, said on X it was a "serious concern for Somalia and the whole of Africa".
Somalia's pointperson for Somaliland, Abdikarim Hussein Guled, said the government in Mogadishu would respond with a "firm and measured statement".
"The Ethiopian government's actions... constitute a blatant disregard for international norms and legal frameworks, representing a brazen violation of Somali territorial sovereignty and undermining the progress achieved through ongoing dialogue beteeen FGS (federal government of Somalia) and Somaliland that was nearing a resolution," Guled said on X.
"This unilateral act jeopardises regional stability and demonstrates a callous disregard for the Somali people's aspirations for peace and self-determination."
The deal comes months after Abiy said his country, Africa's second most populous, would assert its right to access the Red Sea, sparking concerns among its neighbours.
Ethiopia was cut off from the coast after Eritrea seceded and declared independence in 1993 following a three-decade war.
Addis Ababa had maintained access to a port in Eritrea until the two countries went to war in 1998-2000, and since then Ethiopia funnels most of its trade through Djibouti.
Ethiopia's economy has been constrained by its lack of access to the Red Sea, a narrow strip of water between Africa and the Arabian Peninsula.
On the southern coast of the Gulf of Aden, the port of Berbera in Somaliland offers an African base at the gateway to the Red Sea and further north to the Suez canal.
Abiy's national security adviser Redwan Hussein said Ethiopia would have access to a leased military base on the Red Sea as part of the agreement.
It was not clear when the pact would take effect.
In 2018, Ethiopia acquired a 19 percent stake in the Berbera port, according to Dubai-based DP World, which manages the port's operations.
The company itself holds a 51 percent stake, while Somaliland has the remaining 30 percent.
On Friday, Somalia and Somaliland agreed to resume dialogue after two days of talks mediated by Djibouti President Ismail Omar Guelleh, the first of their kind since 2020 when similar negotiations stalled.
The deal was welcomed by IGAD, the regional East Africa grouping which Somalia joined only in November, and the British embassy which described it as a "vital step towards reconciliation".
Somaliland, a former British protectorate with 4.5 million people, prints its own currency, issues its own passports and elects its own government.
Although Somaliland has often been seen as a beacon of stability in the chaotic Horn of Africa region, its quest for statehood has gone unrecognised internationally, leaving it poor and isolated.
Political tensions also surfaced there last year, spilling over into deadly violence.
