Shares in a U.K. oil company with interests in the Falklands have slumped after a U.N. decision that Argentina claims will expand its maritime territory in the South Atlantic Ocean to include the islands.

Rockhopper Exploration PLC shares were down 5.3 percent to 27.00 pence early Tuesday after Argentina said the U.N. Commission on the Limits of the Continental Shelf sided with Buenos Aires.

Argentina says its maritime territory has expanded by 35 percent to include what it calls the Malvinas. Britain, which is responsible for defense and foreign affairs for the islands, has not yet commented.

The Falkland Islands government is seeking clarification from the U.K. on the implications of the U.N. ruling.

Argentina lost a 1982 war with Britain after Argentine troops seized the South Atlantic archipelago.