The UK wants control of this seabed
The UK is laying claim to more than 200,000 square kilometres of mineral-rich seabed in the Atlantic Ocean.
The Foreign Office confirmed a formal bid for the area surrounding Ascension Island has been submitted to the United Nations.
The UN Commission for the Limits of the Continental Shelf (CLCS) will review the claim in August.
No other countries are expected to challenge the bid.
A Foreign Office spokesman said the claim was part of an attempt to establish the limits of continental shelf boundaries and did not mean an extension of "territorial sovereignty".
He confirmed the bid was for seabed beyond 200 nautical miles of Ascension Island - a dependency of the British overseas territory of St Helena. It is located just south of the equator in the South Atlantic Ocean.
He said doing this was perfectly acceptable under international law, and it was the second attempt in two years by the UK to stake a claim for parts of the seabed.
In 2006, the UK made a joint claim with France, Ireland and Spain for an area in the Bay of Biscay.
The spokesman said: "This is the first submission in respect of an overseas territory.
"Ascension Island is a dependency of St Helena, and the UK is responsible for submitting any such claims in respect of its overseas territories."
The UK is also considering whether to make similar claims relating to two other areas, around Rockall and the Falklands, but has until May next year to inform the CLCS of its intentions.
Last year, exploration firms announced their intention to begin drilling the South Atlantic ocean bed surrounding the Falklands to try to prove the region is rich in oil reserves.
Other countries including Canada and Barbados have also begun laying claim to various parts of the continental shelf beneath the world's oceans.
Nation states are allowed to apply to extend their territorial rights over the seabed up to 350 miles from any adjacent coastline.