Fighting has erupted between the forces of the self-declared Somaliland Republic and those of Puntland, an autonomous region of Somalia.
The clashes broke out on Wednesday near the town of Las Anod in Sool, one of two areas claimed by both regions.
A BBC correspondent says it is the first time forces from the neighbouring regions have fought each other.
Meanwhile, the UN has warned of a possible famine if fighting continues in southern Somalia.
Rival warlords have been fighting near the port of Kismayo, disrupting efforts to help those affected by the region's drought.
"Unless the conflict can be stopped very soon, we could be witness to the kind of famine conditions experienced in 1992," said United Nations Humanitarian Coordinator Maxwell Gaylard in a statement issued in the Kenyan capital, Nairobi.
Both Puntland and Somaliland blame the other for starting the hostilities in Sool.
Puntland says it lost one soldier in the battle, says the BBC's Mohamed Olad Hassan in the Somali capital, Mogadishu.
There are no other details on casualties.
Fighting around Kismayo is disrupting aid efforts
Somaliland claims to have captured three Puntland militiamen.
Up to eight armoured vehicles belonging to Somaliland were involved in the clashes, our correspondent says.
Somaliland's Foreign Minister Edna Adan Ismael said the fighting started when food aid was being distributed.
"It's not a war, it was a chasing away of bandits who were trying to disrupt and cause enough confusion to loot rations," she told the BBC's Network Africa programme.
Both regions also claim Sanaag, to the north of Sool.
Somaliland refuses to take part in Somalia's peace process in neighbouring Kenya, where a transitional parliament was sworn in last month.
Somalia has been without a functioning national government since the overthrow of President Mohammed Siad Barre in 1991.