The UN’s top court has ruled largely in favour of Somalia in its long-running dispute with Kenya over their maritime border.
Kenya previously accused the International Court of Justice of bias and said it will not accept the ruling.
The case concerned a 38,000 sq mile (100,000 sq km) triangle in the Indian Ocean that is thought to be rich in oil and gas.
The dispute has been at the heart of a diplomatic row between the neighbours.
In a tweet, Somalia’s Information Minister Osman Dubbe welcomed the ruling and congratulated Somalis on regaining their territory.
For the past four decades, Kenya has said a line due east of the point where the two countries meet at the coast represents the maritime border.
Somalia, however, argued in court that the sea frontier in the Indian Ocean should follow on in the same direction as the land border.
The panel of 14 judges sitting in The Hague said that Kenya had not proved that Somalia had previously agreed to its claimed border.
Instead, they drew a new line which has split the disputed area in two.
But with Kenya refusing to recognise the ICJ’s jurisdiction it is not now clear what will happen. The court has no means to enforce its rulings.
Somalia had also argued that Kenya had violated its sovereignty by operating in its territorial waters and demanded reparations.
The judges, however, rejected this argument.
In 2009, the two countries had agreed in a memorandum of understanding, backed by the UN, to settle the boundary dispute through negotiation.
But five years later, Somalia said the talks had failed and it went to the ICJ instead. The Reuters news agency reports that Somalia was angered by Kenya selling exploration licenses in the disputed zone to two multinationals in 2012.
Speaking before the judgment was delivered, Somalia’s Deputy Prime Minister Mahdi Mohamed Guled told the BBC that his country “believes in the rules-based system… that’s why we came to the court”.
The court is supposed to be the final arbiter in disputes between nations.
If Kenya ignores the ruling, the issue could be escalated to the UN Security Council, reports the BBC Anna Holligan from The Hague.
Kenya argued unsuccessfully that the ICJ should not be involved as the memorandum of understanding was binding.
Then in March it refused to take part in hearings after having asked for a delay to brief a new legal team.
It also objected to the presence on the ICJ panel of a Somali judge, saying he should recuse himself.
Last week, Kenya’s government described the case as a “flawed judicial process”. It added that there was “inherent bias” and that the court was an unsuitable way to resolve the dispute.