At least four soldiers were killed after Ugandan and South Sudanese troops clashed in a disputed border area, Ugandan military officials confirmed Wednesday.

Ugandan military spokesperson Maj. Gen. Felix Kulayigye said the firefight broke out Monday in the West Nile region after South Sudanese soldiers allegedly crossed into Ugandan territory, set up camp, and refused to withdraw.

One Ugandan soldier was killed, prompting a retaliatory attack in which three South Sudanese soldiers were shot dead.

However, Wani Jackson Mule, a local official in South Sudan’s Central Equatoria state, reported receiving the bodies of five South Sudanese soldiers, suggesting a higher death toll. He described the incident as a “surprise attack” by Ugandan forces in an area South Sudan claims as its own.

South Sudanese military spokesman Maj. Gen. Lul Ruai Koang said commanders from both sides have since agreed to an immediate ceasefire to allow for a joint investigation.

The firefight highlights longstanding tensions over the yet-to-be-finalized demarcation of sections of the Uganda-South Sudan border. Both governments have established a joint border committee, though officials say a final resolution is not expected until 2027.

While border skirmishes have occurred sporadically over the years, direct armed confrontations between the two militaries are rare.

Uganda and South Sudan are close allies, with Ugandan troops deployed in Juba and other parts of South Sudan to support President Salva Kiir’s government against forces loyal to Vice President Riek Machar.