Kenya and Somalia have been in feud since 2014 over a demarcation between the countries, where the question was where the border should be drawn in the Indian Ocean.
When the International Court of Justice in The Hague (ICJ) on Tuesday ruled in the case, it was met with outrage in Kenya, which gets only a small part of the coveted area.
"This reverses all the social, political and economic progress that has been made (between the countries) and risks threatening peace and exacerbating the fragile security situation in the whole of the Horn of Africa," said Kenyan President Uhuru Kenyatta, who opposed what he called "biased" court decision, a decision he does not intend to recognize.
"Respect international law"
The ICJ ruled in favor of Somalia and gives the northern neighbor in the feud the right to the waters under which large gas and oil discoveries are believed to exist.
Somalia, for its part, calls on Kenya to "respect international law" and President Mohamed Abdullahi Mohamed says in a televised speech that the ruling gave the countries an opportunity to strengthen their ties.
The court agreed with its decision on the issue of how the border should be drawn in the water - follow the border, as Somalia believes, or straight east, as Kenya thinks.
Between the countries' proposals is 100,000 square kilometers of water, an area Kenya has considered its own since 1979.
Can not be appealed
The ICJ's ruling cannot be appealed, but in practice the court also has no way of ensuring that the ruling is complied with.
If any other nation other than Kenya does not accept the ruling and does not act on it, the issue can be raised in the UN Security Council.
The issue has been infected for a long time, and in 2019 Kenya called home its ambassador to Somalia after accusing the neighbor in the north of having already sold oil and gas fields in the area.