The separatist region of Somaliland on Sunday accused Somalia of attacking its soldiers, despite a ceasefire imposed after heavy fighting in a contested border town earlier in the week.
Somaliland, which has claimed independence from Somalia since 1991, has never been recognised internationally but is often seen as a beacon of stability in a chaotic region.
However, political unease has mounted in recent months.
This week, the United Nations said at least 20 people had been killed in the disputed town of Las Anod in clashes between Somaliland’s armed forces and militias loyal to the central government of Somalia.
On Sunday, the authorities in the Somaliland capital Hargeisa said: “This morning, armed forces from the federal government of Somalia began attacking Somaliland’s military forces.”
They gave no information on possible casualties but said they had issued a warning to Somalia and urged the international community to put pressure on Mogadishu “to withdraw their forces from Somaliland’s border”.
The government in Mogadishu did not make any official response on Sunday morning.
Fighting broke out on Monday in Las Anod, which is situated on a key trade corridor and is claimed by both Somaliland and neighbouring Puntland, a semi-autonomous state of northeastern Somalia.
The violence erupted a few hours after traditional elders in the Sool region, where Las Anod is located, issued a statement pledging support for “the unity and integrity of the Somali Federal Republic” and urged Somaliland authorities to withdraw their soldiers from the area.
On Friday evening, the Hargeisa authorities decreed a ceasefire but on Saturday accused militias loyal to Mogadishu of breaking the truce by attacking its soldiers.
It is unclear how many people have been killed in the recent flare-up.
The UN on Tuesday put the toll at least 20 and demanded an official inquiry.
On Saturday the Red Cross tweeted that one of its volunteers had been shot dead.
It called for “restraint and access (for) neutral and impartial humanitarian actors”.
Somaliland, a region of 4.5 million people, is a former British protectorate.
It prints its own currency, issues its own passports and elects its own government but its quest for statehood has gone unrecognised, leaving it poor and isolated.
The region has been relatively stable in comparison to Somalia, which has witnessed decades of civil war and Islamist insurgency.