THE HAGUE, September 2, 2008 (AFP) - A decades-long dispute between Romania and Ukraine over boundaries in a hydrocarbon-rich zone of the Black Sea entered a new phase Tuesday when it came before the UN's highest court in The Hague.

Romania fired the opening volley at the start of two weeks of public hearings, accusing Ukraine of having shown bad faith in years of failed bilateral negotiations aimed at drawing new maritime boundaries.

'It is not the sophisticated nature of this case but the non-compliance of Ukraine with the rules of delimitation that led to the failure of the bilateral negotiations,' foreign affairs official Bogdan Aurescu argued for Romania before a panel of 16 judges of the International Court of Justice.

Romania instituted proceedings against its neighbour in September 2004 after six years of dedicated bilateral negotiations failed to yield a treaty or resolve an issue that has caused rivalry between the states for decades.

The dispute concerns an area of some 14,000 square kilometers (5,400 square miles), and plans by Kiev to create an exclusive economic zone (EEZ) around the small Serpents Island where natural gas and oil deposits are thought to be concentrated.

Romanian experts have estimate the area may contain 100 billion cubic metres of gas.

Serpents Island, a 17-hectare (42-acre) uninhabited islet, belonged to Romania until 1948, when it was ceded to the then Soviet Union.

Romanian authorities objected to Kiev's later efforts to change its legal status by presenting it as an island enjoying 'its own economic life' and thus a right to an EEZ.

Romania has described the island as a 'rock with no source of water or vegetation'.

A court statement said the hearing concerned 'the establishment of a single maritime boundary between the two states in the Black Sea, thereby delimiting the continental shelf and the exclusive economic zones appertaining to them'.

The ICJ is the highest court of the United Nations, set up to rule on disputes between states.