Kenya has recalled its ambassador from Somalia for "urgent consultations" over a maritime border dispute that involves lucrative offshore oil and gas deposits.
"The summons is a consequence of a most regretful and egregious decision by the Government of Somalia to auction off oil and gas blocks in Kenya's maritime territorial area that borders Somalia," a foreign office statement said.
The "unparalleled affront and illegal grab at the resources of Kenya" had taken place at an auction in London on February 7 and would "not go unanswered", it said.
The UN's highest court has been hearing a case brought by Somalia against Kenya about the dispute.
Nairobi previously unsuccessfully argued that the International Court of Justice in The Hague, which rules in disputes between countries, did not have jurisdiction over the case.
Mogadishu's case against Nairobi focuses on an attempt to redraw the sea border which would affect at least three of Kenya's 20 offshore oil blocks.
Somalia says bilateral talks have failed to resolve the spat. A final outcome will significantly impact a new source of revenue for either of the east African neighbours.
Somalia, which lies north of Kenya, wants to continue the frontier along the line of the land border, in a southeast direction.
But Kenya wants the border to head out to sea in a straight line east, along the parallel of latitude, giving it more sea territory.
The disputed triangle of water, which stretches over an area of more than 100,000 square kilometres (40,000 square miles), is believed to hold valuable deposits of oil and gas in a part of Africa only recently found to be sitting on significant reserves.
A relative newcomer to the oil industry but seen as having major potential, Kenya has already awarded three oil blocks to Italian energy company Eni SpA.