Somalia took its maritime border dispute with Kenya to the United Nations' top court on Thursday, which could decide the fate of potentially lucrative oil and gas reserves off east Africa.
The dispute has been simmering for years, keeping investors away because of the lack of legal clarity over who owns potential offshore oil and gas reserves.
The internationally-backed government in Mogadishu is seeking to claw back authority over Somalia's territorial waters, including the area bordering Kenya that is potentially rich in oil and gas deposits.
Kenya, which has had troops in southern Somalia since 2011, first as an invading force and then as part of an African Union peacekeeping force, lays claim to a triangle of water stretching for more than 100,000 square kilometres (40,000 square miles) that Mogadishu also claims.
Nairobi has already awarded exploration contracts to international firms despite the legal uncertainty.
"Somalia requests the court 'to determine, on the basis of international law, the complete course of the single maritime boundary dividing all the maritime areas appertaining to Somalia and to Kenya in the Indian Ocean'," the International Court of Justice (ICJ) said in a statement.
Somalia, which lies to the north of Kenya, wants the maritime border to continue along the line of the land border, to the southeast.
Kenya however wants the sea border to go in a straight line east, giving it more sea territory.
Both countries have recognised the court's jurisdiction, the ICJ said, a prerequisite for cases there to continue.
"Diplomatic negotiations, in which their respective views have been fully exchanged, have failed to resolve this disagreement," the ICJ quoted Somalia as saying in its application.
Kenya's large military presence in Somalia is part of the African Union force supporting the country's fragile government.
Cases at the Hague-based court can take years.
Established in 1945, the ICJ is the UN's highest judicial body and the only one of five principal UN bodies not located in New York.